2013
James W. Cross
ALL RIGHTS RESERVED
EVALUATION AND GENETIC ANALYSIS OF TALL FESCUE
GENOTYPES FOR SUMMER STRESS TOLERANCE
by
JAMES W. CROSS
A Thesis submitted to the
Graduate School-New Brunswick
Rutgers, The State University of New Jersey
in partial fulfillment of the requirements
for the degree of
Master of Science
Graduate Program in Plant Biology
written under the direction of
William A. Meyer
and approved by
________________________
________________________
________________________
New Brunswick, New Jersey
January 2013
ABSTRACT OF THE THESIS
Evaluation and Genetic Analysis of Tall Fescue Genotypes for Summer Stress Tolerance
by JAMES W. CROSS
Thesis Director:
Dr. William A. Meyer
During summer months, overall turf quality of cool-season turfgrasses commonly
deteriorates significantly. This loss in turf quality can mainly be attributed to the
combination of high temperatures and low soil moisture. The combination of these two
stresses is commonly referred to as “summer stress”. Tall fescue (Lolium arundinacea
[Schreb.] Darbysh) exhibits substantial variation in performance under summer stress
between genotypes. The objectives of this thesis were to [1] evaluate diverse tall fescue
genotypes being subjected to heat, drought, and/or combinations of both stresses growing
in a growth chamber, rainout shelter, and under field conditions, and [2] evaluate progeny
of a full diallel cross and polycross block made with tall fescues exhibiting different
degrees of summer stress tolerance.
Twenty-four experimental tall fescue genotypes, twelve summer stress tolerant
and twelve summer stress sensitive, were selected for evaluation while growing under
field conditions during the summer of 2010 at the Rutgers Agricultural Experiment
Station located in Adelphia, NJ. A growth chamber study subjected these genotypes to
heat and drought stress alone and in combination. The performance of genotypes in the
heat stress treatment was similar to the performance of the genotypes under field
ii
conditions, however summer stress tolerant genotypes did not perform significantly better
in the drought or heat + drought treatments. Mowed space-plants of these 24 genotypes
were evaluated while growing in an automatic rainout shelter structure over two years.
Genotypes selected as summer stress tolerant had higher quality ratings than the summer
stress sensitive group. Additionally, quality ratings in the rainout shelter were moderately
correlated with quality ratings in the heat stress growth chamber.
A full diallel cross and a polycross block were used to estimate narrow-sense
heritability values of 0.66 and 0.48, respectively. Heterosis was found to be significant in
40% of the diallel crosses. Data from the diallel and polycross block indicate breeding for
enhanced summer stress tolerance in tall fescue would result in 52% and 32%
improvements per selection cycle, respectively, when making recurrent selections of the
top 5% of the population.
iii
ACKNOWLEDGEMENTS
I would like to thank my advisor, Dr. William A. Meyer, for his unwavering
support, leadership, and assurance throughout my graduate studies. I would also like to
thank my other committee members, Dr. Stacy Bonos and Dr. Bingru Huang; without
their insight and assistance along the way, I would have been lost.
My sincerest appreciation goes to the Center for Turfgrass Science, the Henry
Indyk Graduate Fellowship, the Ralph Geiger Scholarship, and the Peter S. Loft
Memorial Scholarship for their financial support throughout my graduate work.
My special thanks to Ron Bara, Dirk Smith, and Melissa Mohr. I learned far more
from the three of you than I learned in any class. Your tireless efforts to mentor and teach
me went far beyond your jobs’ responsibilities. For your selfless help along the way, I
will be forever thankful.
Lastly, I would like to thank Eugeniusz Szerszen, Patrick Burges, Matt Bara,
Ryan Daddio, Brian Dzugan, Eric Koch, James Hempfling, Priti Saxena, Vinnie
Averallo, George Ziemienski, James Schumacher, Joe Florentine, Mark Peacose, Jeff
Akers, and David Learn who were there to lend a helping hand, a piece of advice, or a
word of reassurance along the way. Though your actions may have seemed insignificant
to you, they were invaluable to me.
iv
TABLE OF CONTENTS
ABSTRACT OF THE THESIS ...................................................................................
ii
ACKNOWLEDGEMENTS .........................................................................................
iv
TABLE OF CONTENTS .............................................................................................
v
LIST OF TABLES ....................................................................................................... viii
LIST OF FIGURES .....................................................................................................
x
CHAPTER 1: Literature Review .............................................................................
1
INTRODUCTION ...........................................................................................
1
TALL FESCUE ...............................................................................................
5
DROUGHT ......................................................................................................
7
HEAT. ..............................................................................................................
11
SUMMER STRESS .........................................................................................
14
BREEDING FOR SUMMER STRESS ...........................................................
15
SUMMARY AND OBJECTIVES ...................................................................
21
LITERATURE CITED ....................................................................................
22
CHAPTER 2: Evaluation of Heat and Drought as Components of Summer Stress on
Tall Fescue Genotypes ...............................................................................................
28
INTRODUCTION ...........................................................................................
30
MATERIALS AND METHODS .....................................................................
33
Plant Material .......................................................................................
33
v
Data Collection ....................................................................................
34
RESULTS AND DISCUSSION ......................................................................
37
CONCLUSIONS..............................................................................................
42
LITERATURE CITED ....................................................................................
43
CHAPTER 3: Field Testing of Summer Stress Tolerance in Tall Fescue Using a
Rainout Shelter Structure .........................................................................................
50
INTRODUCTION ...........................................................................................
52
MATERIALS AND METHODS .....................................................................
55
Plant Material .......................................................................................
55
Statistical Analysis ...............................................................................
57
RESULTS AND DISCUSSION ......................................................................
59
CONCLUSIONS..............................................................................................
64
LITERATURE CITED ....................................................................................
65
CHAPTER 4: Inheritance of Summer Stress Tolerance in Tall Fescue ...............
77
INTRODUCTION ...........................................................................................
78
MATERIALS AND METHODS .....................................................................
81
Plant Material .......................................................................................
81
Breeding ...............................................................................................
81
Diallel Cross.............................................................................
81
Polycross ..................................................................................
82
Field Planting and Evaluation ..............................................................
83
vi
Statistical Analysis ...............................................................................
85
RESULTS AND DISCUSSION ......................................................................
87
CONCLUSIONS..............................................................................................
93
LITERATURE CITED ....................................................................................
94
CHAPTER 5: Thesis Conclusions ............................................................................ 102
vii
LIST OF TABLES
CHAPTER 2
2.1
Quality ratings (1-9 visual ratings scale) of tall fescue genotypes evaluated
under heat, drought, heat and drought and control treatments in a growth chamber.
Field rating signifies plants selected under field conditions as summer stress
tolerant (T) or summer stress sensitive (S) ......................................................
2.2
45
Relative water content readings (percentage of water in leaves compared
to fully turgid leaves) of tall fescue genotypes evaluated under heat, drought, heat
and drought and control treatments in a growth chamber. Field rating signifies
plants selected under field conditions as summer stress tolerant (T) or summer
stress sensitive (S) ............................................................................................
2.3
46
Table 2.3. Electrolyte leakage readings (%) of tall fescue genotypes
evaluated under heat, drought, heat and drought and control treatments in a
growth chamber. Field rating signifies plants selected under field conditions as
summer stress tolerant (T) or summer stress sensitive (S) ..............................
47
CHAPTER 3
3.1
Analysis of variance of summer stress tolerance of 24 tall fescue clones
evaluated over 2 years (2011 and 2012) in a rainout shelter structure at the
Rutgers Agricultural Experiment Station in Adelphia, New Jersey ................
68
CHAPTER 4
4.1
Description of diallel crosses between summer stress tolerant and summer
stress sensitive tall fescue genotypes, includes heterosis calculations ............
viii
97
4.2
Description of polycross block using three summer stress tolerant and
three summer stress sensitive tall fescue genotypes ........................................
4.3
98
Calculations of maternal effects and minimum gene number estimation in
the full diallel cross ..........................................................................................
ix
99
LIST OF FIGURES
CHAPTER 2
2.1
Turf quality (a), photochemical efficiency (b), relative water content (c)
and electrolyte leakage (d) of summer stress tolerant and sensitive tall fescue
genotypes evaluated under heat, drought, heat and drought and control treatments
in a growth chamber. Error bars indicate LSD values (P=0.05). The treatment and
rating week in which the data was taken are shown on the x-axis ..................
48
CHAPTER 3
3.1
Comparison of visual quality ratings during the summer of 2012 between
replications of 24 tall fescue genotypes growing in a rainout shelter structure at
the Rutgers Agricultural Experiment Station in Adelphia, New Jersey. Error bars
represent LSD at P=0.05. ................................................................................
3.2
69
Clone quality distribution of tall fescue clones growing in a rainout shelter
at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey on
October 26, 2011 (a) and June 25, 2012 (b) ....................................................
3.3
70
Comparison of quality distributions of clones previously selected as
summer stress tolerant or sensitive. Quality ratings of plants growing in a rainout
shelter at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey on
October 26, 2011 (a) and June 25, 2012 (b) ....................................................
3.4
71
Comparison of visual quality ratings over time during the summer of 2011
of tall fescue clones selected as summer stress tolerant or summer stress sensitive
x
growing in a rainout shelter at the Rutgers Agricultural Experiment Station in
Adelphia, New Jersey. Error bars represent LSD at P=0.05. ..........................
3.5
72
Comparison of visual quality ratings over time during the summer of 2012
of tall fescue clones selected as summer stress tolerant or summer stress sensitive
growing in a rainout shelter at the Rutgers Agricultural Experiment Station in
Adelphia, New Jersey. Error bars represent LSD at P=0.05. ..........................
73
3.6
Daily atmospheric temperature ranges from May 16 – August 6, 2012 at
the
Rutgers Agricultural Experiment Station, Adelphia, NJ. Average quality
ratings of all tall fescues growing the rainout shelter on each of the six rating
dates are also shown. ...................................................................................................
3.7
74
Daily atmospheric temperature ranges from September 1 - October 31,
2011 at the Rutgers Agricultural Experiment Station, Adelphia, NJ. Average
quality ratings of all tall fescues growing the rainout shelter on each of the three
rating dates are also shown.............................................................................
3.8
75
Rainout shelter-growth chamber correlation of clonal averages of 24
clones grown in both a rainout shelter at the Rutgers Agricultural Experiment
Station in Adelphia, NJ and growth chamber heat stress treatment. Rainout shelter
quality ratings are averages for each clone over 2 years. Growth chamber quality
ratings are averages for each clone on the final rating date in the heat chamber. 76
CHAPTER 4
4.1
Progeny quality distribution for full diallel cross (a) and polycross block
(b), during the summer of 2012 at the Rutgers Agricultural Experiment Station in
xi
Adelphia, New Jersey ...................................................................................... 100
4.2
Mid-parent-progeny regression of six tall fescue parents crossed in a full
diallel design (a) and a polycross design (b) evaluated for summer stress tolerance
observed during the summer of 2012 at the Rutgers Agricultural Experiment
Station in Adelphia, New Jersey ...................................................................... 101
xii
1
CHAPTER 1
Literature Review
INTRODUCTION
Turfgrass is one of the most versatile plant based ecosystems in existence; being
used for erosion control, countless forms of recreation, transportation thoroughfares,
oxygen production, and beautification (Turgeon, 2005). Turfgrass also has the ability to
act as an effective buffer of harmful chemicals, such as pesticides, when used along
roadways and agricultural fields (Borin, 2005). In New Jersey, more than 18% of the
state’s total land is turf, and of those 880,542 total acres, ≈ 75% are home lawns
(Govindasamy et al., 2007). New Jersey is not alone in having a huge amount of land
covered by turf; Florida was estimated to have ≈ 13% of its total land covered by 4.4
million acres of turf, and ≈ 75% being made up of home lawns (Hodges et al., 1994).
Studies have estimated that in the United States, ≈ 27.6 million acres of land are turf
covered (Bormann et al., 2001). In the years since this estimate was made, the lawn
component of total turf area in the United States was estimated to grow by more than
380,000 acres each year (Robbins and Birkenholtz, 2003).
A visionary for his time, Dr. Howard B. Sprague began a program for genetic
improvement of turfgrasses at Rutgers University just prior to World War II. One of Dr.
Sprague’s first projects focused on velvet bentgrass (Agrostis canina L.), which he found
intriguing due to its ability to produce a high quality turf with minimal inputs. In 1940,
this led to the release of a variety called ‘Raritan’ velvet bentgrass. The release of
‘Raritan’ as well as some other major developments (‘Merion’ Kentucky bluegrass [Poa
pratensis L.] and ‘Meyer’ zoysiagrass [Zoysia japonica Steud.]) were met with such
2
interest that, following the World War II, Rutgers quickly reestablished its turfgrass
program. In addition to education and extension relating to turfgrass management, an
emphasis was placed on the genetic improvements of turfgrasses. This emphasis, coupled
with the realization that there was a great need for turfgrasses better adapted to the
climate of the Eastern United States led to the hire of Dr. C. Reed Funk as the first full
time turfgrass breeder at Rutgers University in 1961. Since that time, Dr. Funk and
eventually Dr. William A. Meyer have grown the Rutgers turfgrass breeding program
from one with a $400 budget and the part-time use of a university vehicle, into one that is
able to fund its research through royalties from cultivars it has produced (Funk and
Meyer, 2001). The Rutgers turfgrass breeding program is currently the world leader and
has been involved in the development of countless top performing cultivars.
Cool-season, commonly referred to as “C3”, turfgrasses are more sensitive to hot
and dry conditions than warm-season, “C4” grasses. The variation in summertime
performance between these grasses is a result of differences in their photosynthetic
process. While both C3 and C4 photosynthesis use carbon molecules from CO2 to form
complex sugars, variation in both the method of initial CO2 processing, as well as where
carbon fixation occurs, make the processes significantly different (Turgeon, 2005). C3
photosynthesis occurs in leaf mesophyll cells and relies on a steady supply of CO2
entering through stomata. In the mesophyll cells, CO2, ribulose bisphospahte (RuBP), and
H2O are carboxylated by 1,5-bisphosphate carboxylase (rubisco) to produce O2 and the
three carbon compound called 3-phosphoglyceric acid (PGA)(Fry and Huang, 2004). The
resulting PGA is then reduced to form a three-carbon sugar. This process is efficient
while CO2 concentrations are high; however, if diffusion is not able to maintain high CO2
3
levels in the mesophyll cells, photorespiration will begin to dominate (Tiaz and Zeiger,
2002). Photorespiration is a wasteful process that occurs due to rubisco’s ability to
catalyze oxidation of RuBP in the presence of oxygen.
C4 plants avoid photorespiration in a number of ways including: 1) performing the
carbon fixation steps of photosynthesis in bundle sheath cells away from high O2
concentrations, 2) saturating bundle sheath cells with CO2 in the form of malate, and 3)
phosphoenolpyruvate (PEP), a carboxylation catalyst used by C4 plants, cannot react with
oxygen like rubisco can (Fry and Huang, 2004). During high temperatures and/or dry
conditions, plants close stomata in order to prevent water loss. While C4 plants are able to
continue to actively photosynthesis, stomatal closure causes a rapid decline in CO2 levels
in C3 plants (Taiz and Zeiger, 2002). As the CO2:O2 ratio drops; rubisco begins reacting
with 02, causing photorespiration and an overall loss of energy from the plant (Fry and
Huang, 2004).
Summertime temperatures in a large part of the United States are regularly
supraoptimal for cool-season turfgrasses and would favor the use of warm-season
turfgrasses. This is, however, not an option due to the limited cold hardiness of warmseason species. Even warm-season grasses exhibiting high levels of cold hardiness like
Zoysiagrass, classified as “very good” , and bermudagrass, classified as “good” are only
estimated to survive down to -14° C and -8° C respectively (Fry and Huang, 2004). In
most of the Northern United States, where temperatures below these marks are not
uncommon during winter months, cool-season grasses are the only option (Turgeon,
2005).
4
Special care must be taken to manage them during summer months in order to
maintain cool-season turfgrasses. Many cultural practices including, irrigation, mowing,
fertilization, cultivation, topdressing, and the use of plant growth regulators, can affect a
turfgrass’ performance under both heat and drought stress (Fry and Huang, 2004). Even
with proper management, summer stress still causes a significant decline in the quality of
cool-season turfgrasses. The use of superior species and improved varieties is becoming
increasingly important as water restrictions become more common. Among cool-season
turfgrasses, tall fescue is considered one of the best options for performance under
summer stress (Beard, 1973). Fry and Huang (2004) categorized tall fescue as having
“very good” relative heat resistance, “very good” overall drought resistance, and
“excellent” drought avoidance.
5
TALL FESCUE
Tall fescue [Lolium arundinacea (Schreb.) Darbysh.], like most turfgrasses used
in this country, is not native to the United States (Burton, 1969). Tall fescue was brought
to North America in the late 1800s from its center of origin in wet pastures of Western
Europe and Northern Africa (Buckner et al., 1979). At first, tall fescue was considered a
grass of little significance, however near the turn of the 20th century, following an
outbreak of “oat” rust (Puccinia coronata F. sp. avenae.) which devastated meadow
fescue (Festuca pratensis), interest in tall fescue grew due to its resistance to crown rust
(Buckner et al., 1979). Still, it was not until the releases of ‘Alta’ and ‘Kentucky 31’ in
1940 and 1943, respectively, that tall fescue use exploded (Meyer and Funk, 1989). Over
the next 30 years tall fescue replaced meadow fescue as the predominant forage grass and
even became the most widely used cool-season perennial turfgrass (Buckner et al., 1979).
Prior to these releases, tall fescue was grown on approximately 40,000 acres in the United
States; 30 years later, in 1973, it was growing on more than 30,000,000 acres nationwide
(Buckner et al., 1979). Tall fescue has been recommended for use from the Northeast to
the Southwest because of its ability to grow in a wide range environmental conditions,
especially in difficult “transition zone” climates (Hannaway et al., 2009; Meyer and
Funk, 1989).
Early tall fescue culture and use can be summed up simply, by the
recommendations of Sprague in an early edition of his Turf Management Handbook.
Sprague (1982) described tall fescue as a very coarse larger relative of meadow fescue,
which is unable to tolerate being mowed lower than 3-4 inches. This description was
correct until Reed Funk released a landmark cultivar called ‘Rebel’ in 1980 (Funk and
6
Meyer 2001). ‘Rebel’ was the first tall fescue that was classified as “turf-type”, differing
from past releases such as ‘Kentucky 31’ and ‘Alta’ in that it had finer darker leaves,
slower vertical growth rate, and the ability to grow more leaves per unit area making it
much denser (Brede, 2000). In the 1980s, even more diminutive, slower growing tall
fescues were developed and began to enter the market; they were deemed “dwarf-type”
tall fescues (Brede, 2000). Dwarf and turf-type tall fescues have lower water usage rates
than forage-types (Carrow, 1996). While they lack the high water usage typical of foragetype tall fescues (Biran et al., 1981), it should not be automatically assumed that they
have a higher level of drought tolerance. In comparisons of dwarf-, turf-, and forage-type
tall fescues, turf and forage types have been shown to perform significantly better in
drought conditions (Meyer and Watkins, 2003; Huang et al., 1998; Carrow, 1996).
7
DROUGHT
Turfgrass drought resistance is considered the ability to continue growing and not
enter dormancy during times of limited water availably (Burton et al., 1954).
Mechanisms for drought resistance in turfgrasses can be characterized as either root
characteristics allowing for increased water uptake, shoot characteristics limiting water
loss, or simply having a high root to shoot ratio ensuring that roots do not have to supply
water to too many shoots (Karcher et al., 2008; Kramer, 1980; Levitt, 1980).
The two most important characteristics necessary for turfgrass to access enough
water during drought, are a high root: shoot ratio and a deep root system (Kramer,
1980).Tall and hard fescue are both highly drought tolerant grasses, however, their
mechanisms for this tolerance are very different. Brar and Palazzo (1995) worked to
evaluate and characterize the drought tolerance of these two species. ‘Clemfine’ tall
fescue and ‘Reliant’ hard fescue were grown from seed in 20-cm deep pots in a
greenhouse for 45 days before stress treatments were initiated. The drought treatments
were 7, 14, and 21 days without irrigation. This study found that tall fescue and hard
fescue both tolerated the drought stress well, but do so in different ways. Hard fescue was
found to have shallow roots, slow growth rate, and a low water use rate. Tall fescue grew
far more rapidly, had deeper more expansive roots, and had a high water use rate.
Sheffer et al. (1987) designed an experiment to evaluate the rooting characteristics
and water uptake abilities of three cool-season turfgrass species. Early cultivars,
‘Fylking’ Kentucky bluegrass, ‘Manhattan’ perennial ryegrass (Lolium perenne L.), and
‘Kentucky 31’ tall fescue, were selected for use in this experiment. Using labeled 32P,
differences in water uptake, and its subsequent translocation to leaf tissue, was observed.
8
The differences in 32P uptake were interestingly not strongly correlated with rooting
patterns, indicating that this was not a good method of evaluating soil water uptake. Tall
fescue was found to have less root mass in the upper 12-cm of the soil profile than
Kentucky bluegrass, and as a result had the highest soil water content in top 6-cm of the
soil. These findings are opposite of the findings deeper in the soil profile. In all four of
the measurements taken below 36-cm tall fescue was found to have the highest root mass.
Tall fescue also had the lowest soil water content at both the 54-cm and 78-cm
measurement depths. The percentage of root mass that was found below 36-cm was
10.6% for tall fescue, 7.4% for perennial ryegrass, and only 2.5% for Kentucky
bluegrass.
A low baseline evapotranspiration is connected with increased performance under
drought conditions (Beard, 1989), however this is not the only factor contributing to a
plant’s overall drought performance. High levels of root growth and increased ability for
water uptake from deep in the soil profile are strongly correlated with good drought
tolerance (Huang and Gao, 2000).
The low level of drought tolerance of dwarf-type tall fescue has been attributed to
a shallow root length, with their roots primarily occupying only the top 10-cm of a soil
profile. Forage and semi-dwarf turf-types have much deeper and more expansive root
systems (Carrow, 1996). A high level of variation in drought tolerance exists among turftype tall fescues (Huang and Gao, 1999). In addition, variation exists in the factors
contributing to performance under drought, such as evapotranspiration rate and ability to
acquire soil water (Kopec et al., 1988). ‘Mustang’, a semi-dwarf turf-type, performs very
well under drought conditions even in transition zone climates where it is capable of
9
outperforming various warm-season grasses during summer months in Georgia (Qian et
al., 1997). Turf-type tall fescue performance under drought conditions commonly
exceeds that of forage-types (Huang et al., 1998; Carrow, 1996; White et al., 1993).Tall
fescue’s ability to maintain a deep expansive rooting system, even under regular mowing,
make it an excellent option for areas where drought is common and irrigation is not an
option.
While root characteristics are thought to be most important to overall drought
tolerance in tall fescues (Carrow, 1996), they are not the only part of the plant involved in
water relations. Characteristics of leaves in grasses, as well as a wide array of other
plants, have been shown to be important components contributing to a plant’s
performance under drought (Maricle et al., 2007; Pallardy and Rhoads, 1993; Redmann,
1985; Sinclair et al., 2007). Fu and Huang (2004) conducted a study to determine which
leaf characteristics were associated with superior performance of tall fescues while under
drought stress. Sods, 10-cm in diameter, were harvested from 12 tall fescue cultivars that
had been growing under field conditions for 4 years. All sods were harvested leaving 20cm of soil and roots attached, and moved into a greenhouse. Water was withheld from
plants receiving the drought treatment while the control plants were irrigated as needed.
Leaf characteristics such as stomatal density, epicuticular wax content, leaf width, leaf
thickness, tissue density, guard cell length, and specific leaf area were measured. Under
drought conditions, a strong correlation between high turf quality and both narrow leaf
texture and high tissue density were observed. Thicker leaves and higher amounts of
epicuticular wax were also found to be correlated to higher turf qualities under drought
10
conditions (Fu and Huang, 2004). Drought tolerance is a large factor contributing to the
summer-time performance of tall fescue, however there are other factors involved.
11
HEAT
Drought is not the only stress that negatively affects turfgrasses during summer
months. Beard (1973) explained that high temperatures are a significant component in the
summertime stress of cool-season turfgrasses (Beard, 1973). Shoot growth for coolseason turfgrasses is vulnerable to high temperature with the optimum range being
between 15° and 24° C; in contrast, the optimal range for warm-season shoot growth is
26°-35° C (Beard, 1973). Tall fescue is the grass of choice in the eastern United States,
along the border between the temperate climate of the Northeast and the subtropical
climate of the south. Tall fescue is ideal in this region known as the “transition zone” due
largely to its superior heat tolerance compared to other cool-season grasses and its freeze
tolerance compared to warm-season grasses (Turgeon, 2005). North Carolina, located in
the heart of the transition zone, has more than 1 million acres of maintained tall fescue,
equating to more than 3% of the states total land area (Tredway et at., 2005). Kentucky
bluegrass is another cool-season turfgrass suggested for use in transition zone regions due
to its superior performance under high temperatures when compared to species such as
perennial ryegrass (Werner and Watschke, 1981). Growth chamber studies have
demonstrated that Kentucky bluegrass and hybrid Texas bluegrass (Poa pratensis L. x
Poa arachnifera Torr.) had higher heat tolerance than tall fescue (Sum et al., 2007; Jiang
and Huang, 2001a). These findings are challenged by the superior performance of tall
fescue grown in the field in transition zone climates (Bremer et al., 2006).
Plants cool themselves through evapotranspiration. Tall fescue has the highest
transpiration rate of all common turfgrasses species (Biran et al., 1981; Beard, 1989; Brar
and Palazzo, 1995; Githinji et al., 2009). It is likely that when grown under field
12
conditions, tall fescue’s expansive root system is capable of supplying it with enough
water to efficiently protect itself from heat stress through transpirational cooling. A high
amount of genetically controlled variation in evapotranspiration rates has been found
within tall fescue (Bowman and Macaulay, 1991). The variation in evapotranspiration
rates among tall fescue cultivars is one factor that could explain differences in the
summer performance of tall fescue cultivars.
Sifers and Beard (1993) conducted a study to determine inter- and intraspecific
differences of cool-season turfgrasses growing in high temperature environments. The
study included 137 genotypes from 13 different species and was conducted over two
years in a glass house. They observed both inter- and intraspecific differences between
the grasses whether the temperature increase occurred rapidly or gradually over time.
Both inter- and intraspecific differences were also found when comparing transpirational
cooling ability. They suggested that differing levels of heat tolerance were likely a result
of differences in the plant’s abilities to cool via evapotranspiration. Similar to results of
other heat treatment studies, this experiment found tall fescue and Kentucky bluegrass to
be among the most heat resistant cool-season grasses (Sifers and Beard, 1993). Tall
fescue’s ability to access large amounts of water, coupled with its inherent high rate of
evapotranspiration allow it to cool itself in high temperatures (Biran et al., 1981; Beard,
1989; Brar and Palazzo, 1995; Carrow, 1996; Githinji et al., 2009; Jiang and Huang,
2001b)
Cui et al. (2006) compared the photosynthetic performance of two tall fescue
genotypes known to have differing levels of heat tolerance. ‘Jaguar 3’ (heat tolerant) and
‘TF 66’ (heat sensitive) were heat stressed in growth chambers with day/night
13
temperatures of 35° C/30° C for twenty days. They found that maintenance of
photosynthesis, more specifically the maintenance of photosystem II and chlorophyll
content, was very important in tall fescue’s ability to survive during high temperatures.
They also found that prevention of cell membrane damage via antioxidant production was
strongly correlated with heat tolerance.
In a similar experiment by Wang et al. (2009),‘Jaguar 3’ (heat tolerant) and ‘TF
66’ (heat sensitive) cultivars were subjected to heat stress in growth chambers for 20
days with day/night temperatures of 35° C/30° C. The relative growth rate of ‘Jaguar 3’
decreased by 10% at day 20, while the relative growth rate at day 20 for ‘TF 66’
decreased by 93.7%. ‘Jaguar 3’ did not suffer the drastic drop in root to shoot ratio
compared to ‘TF 66’. ‘Jaguar 3’ also had significantly less electrolyte leakage from its
root and leaf tissue cells (Wang et al., 2009).
Heat pre-treatment, as a method of acclimation to future heat stress, was studied
by Xu et al. (2006). Perennial ryegrass and tall fescue were heat pre-treated for 3 days in
a growth chamber at 30 C. Following the pre-treatment, plants were subjected to heat
treatments of 38, 42, or 46 C for 14 hours. This study found that acclimation caused
plants to retain higher leaf relative water contents, higher membrane stability, and lower
membrane peroxidation, than those that had not received the pre-treatment. It was also
found that the pre-treated plants had higher levels of metabolites important in plant
antioxidant systems. Tall fescue was shown to endure less membrane damage during heat
treatments than perennial ryegrass regardless of pretreatment. Tall fescue’s ability to
actively grow and photosynthesize even under high temperatures is another factor
contributing to it maintaining a high turf quality during summer months.
14
SUMMER STRESS
High temperatures and lack of rain are common during summer months in much
of the United States. While these two stresses are often present together, it is not
necessarily the case that cool-season turfgrass will become stressed by both to the same
degree even when both stresses are severe (Jiang and Huang 2001a; Jiang and Huang
2001b; Jiang and Huang, 2000). The differentiation of whether a stand of turf is
becoming stressed primarily because of high temperatures or low soil moisture is very
important, as these two stresses must be managed differently (Turgeon, 2005). Therefore,
it is important to separate the two stresses to determine which stress is more important for
turfgrass survival under summer stress conditions.
15
BREEDING FOR SUMMER STRESS TOLERANCE
Tall fescue is an allohexaploid with 2n=6x=42 chromosomes and 3
homoeologous constituent genomes, represented as AABBCC (Jauhar, 1975). Tall fescue
is almost completely self-incompatible (Meyer and Watkins, 2003), with the exception
being rare self-fertile types (Cowan, 1956). Much of the germplasm base for modern day
tall fescue breeding has been collected by Drs. Reed Funk and W. A. Meyer from
pastures and fields throughout the United States (Funk and Meyer, 2001; Meyer and
Watkins, 2003). In order to increase genetic variability, as well as potentially introduce
disease and stress resistance traits, collection trips are being made in Europe, northern
Africa, central Asia, and Siberia, where tall fescue is native (Meyer et al., 2001).
Baird et al. (2012) surveyed the genetic diversity present in modern turf-type tall
fescue. A selection of 93 cultivars from the 2006 National Turfgrass Evaluation Program
(NTEP) was analyzed with 190 polymorphic markers using Diversity Arrays
Technology. Comparisons of the 93 2006 NTEP entries showed a low degree of genetic
diversity, suggesting that all of these entries are closely related. These findings were
made more apparent when analysis of 14 forage-type tall fescues showed much higher
genetic variation than exists between the NTEP turf-types (Baird et al., 2012). The low
amount of genetic diversity found among turf-type tall fescues in the 2006 NTEP (Baird
et al., 2012) epitomizes the importance of introduction of genetic diversity through
collection of ‘wild’ germplasm from Europe and northern Africa as described by Meyer
and Watkins (2003).
Heat and drought stress are significant factors limiting yield and affecting the
productivity and management of countless agricultural crops worldwide (Wrigley et al.,
16
1994; Blum, 1985). Studies of the inheritance of increased heat and drought tolerance in
agriculturally important crops, including monocots, have found that it is a complex
quantitatively inherited trait (De la Peña and Hughes, 2007; Diab et al., 2004). Rebetzke
et al. (2006) found carbon isotope discrimination in bread wheat (Triticum aestivum L.), a
trait previously shown to be negatively correlated to transpirational efficiency, to be
controlled primarily by multiple additive genes. A high degree of additive gene action
was also shown in variation of excised leaf water loss rate and relative water content in
wheat (Dhanda and Sethi, 1998). Research on other monocots such as sorghum (Sorghum
bicolor [L.] Moench) has found that various factors contributing to drought tolerance are
each controlled by multiple genes (Tuinstra et al., 1997).
Bonos et al. (2004) conducted an experiment to determine the efficacy of using a
greenhouse screening protocol to breed for high root to shoot ratios. This experiment was
conducted with both tall fescue and perennial ryegrass. Four original populations were
put through two cycles of recurrent selection, with selections being made for germination
as well as deep root production and low shoot production. The screening for deep rooting
and low shoot production was conducted on plants growing in 5.1-cm diameter x 63.5-cm
long tubes. After an 8-12 week (depending on species) grow-in period, where clippings
were taken and weighed, the tubes were cut at a depth of 30-cm. The roots from below
30-cm of each tube were washed and weighed. Selections were made of the best 2-4% of
each population. The requirements for selection included having a root mass at least one
standard deviation above the mean in the below 30-cm depth as well as having clipping
yield less than or equal to the population mean. This study found gains in root mass in the
lower 30-cm, after two selection cycles, of 41% for the population with a narrow genetic
17
base and 81% for the population with a broad genetic base. Gains from this method of
selection were even larger in the two populations of perennial ryegrass, with gains of
130% and 376%.
Karcher et al. (2008) continued additional studies, under field conditions, for the
drought tolerance of plants selected in the experiment above. They compared the drought
tolerance of plants selected in greenhouse screening to have a high root-to-shoot ratio to
plants that had been selected as drought tolerant while growing under severe drought
conditions in the field. Selections of plants based on high root-to-shoot ratios in the
greenhouse exhibited more consistent drought tolerance than field-selected plants. The
authors suggest that selection for higher root shoot ratios in the greenhouse was
ultimately a better selection method for drought tolerance in tall fescues.
Carrow and Duncan (2003) evaluated a unique selection protocol for increasing
the drought resistance in tall fescue. The protocol had three distinct steps and was first
explained by Duncan and Carrow (1997). The first step of the process was to make
selections of plants performing well under field conditions while being subjected to
multiple abiotic stresses. Crosses were then set up between plants selected in step 1. The
third and final step was to screen the progeny while they were subjected to further abiotic
stresses as well as edaphic stresses and scalping stress. Carrow and Duncan (2003) found
that they were able to make significant improvements in the drought tolerance of tall
fescue by selecting plants during these intense and diverse stress conditions.
Traditional breeding techniques have been used to produce new, superior
performing, tall fescue cultivars for decades. These practices use tall fescue’s selfincompatibility and cross-pollinating nature to produce large populations of genetically
18
unique half-sibling progeny from a cross of as few as 50 selected parents (Meyer and
Watkins, 2003).
Tall fescue can be used as a parent in several interspecific hybridizations
including crosses with annual ryegrass (Lolium multiflorum Lam.), giant fescue [Festuca
gigantean (L.) Vill.], and perennial ryegrass (Meyer and Watkins, 2003). Interspecific
hybrids have been made to incorporate useful traits into tall fescue as well as into other
species from tall fescue (Asay et al., 1979; Buckner et al., 1976; Buckner et al. 1961).
Traditional breeding practices have transformed tall fescue from ‘Kentucky 31’, a
coarse, lime-green, forage grass which is consistently the lowest performing tall fescue
evaluated at the Rutgers New Jersey turfgrass trails, into a dark green, fine textured
turfgrass capable of matching if not exceeding the turf quality of high performing
Kentucky bluegrasses (Bokmeyer et al. 2004). The transformation of tall fescue from
‘Kentucky 31’ into what it is today has taken more than 70 years. Contemporary breeding
techniques offer a great deal of potential to aid and accelerate the traditional turf breeding
process. Molecular tools such as marker assisted section (MAS) and gene transfer have
the potential to greatly increase the rate and amount of genetic improvements to tall
fescue (Meyer and Watkins, 2003).
Recent construction of a genetic linkage map, through the use of amplified
fragment length polymorphisms (AFLP) and expressed sequence tag simple sequence
repeats (SSR), will be extremely valuable to breeders attempting to use MAS (Saha et al.,
2007; Saha et al., 2005). The map developed by Saha et al. (2005) is a significant
improvement to previous genetic linkage maps available for tall fescue because, in
addition to it being constructed with PCR-based markers, it is more precise and covers
19
more of the genome. Various quantitative trait loci (QTL) have been identified for forage
characteristics in tall fescue (Saha et al., 2007); however, to date there is no reliable QTL
library relating to tall fescue turf characteristics. The use of MAS in tall fescue, and
turfgrass breeding as a whole has been quite limited due to factors such as the complexity
of both the desired traits and the genomes of turfgrasses as well as the difficulty in
accurately and consistently phenotyping the genetic material (Zhang et al., 2006). While
inherent difficulties exist, there is also the potential for increasing the rate at which
improvements in heat and drought tolerance can be made. The use of MAS also has the
potential to help remove the presence of unwanted traits by eliminating linkage drag
(Sleper and Poehlman, 2006).
In 2003, Wang et al. tested the viability of genetically transformed tall fescues
under field conditions. A gene gun was used to generate transgenic lines of ‘Kentucky31’ tall fescue. This experiment found transgenic tall fescue plants had significantly
lower overall performance than seed produced control ‘Kentucky-31’ progeny. However,
the progeny of the transgenic plants had a performance similar to the progeny of seed
produced plants. This suggests that genetically transformed tall fescues could be
integrated into classical breeding programs (Wang et al., 2003). Other methods of gene
transformation, such as Agrobacterium-mediated transformation, have been shown to be
effective, reliable, and efficient in tall fescue as well (Dong and Qu, 2005). Genetic
transformation has been used to produce transgenic tall fescue plants which
express/overexpress select genes from Arabidopsis resulting in increased tolerance to
drought (Zhao et al., 2007) and heat (Kim et al., 2010) stresses. Both of these
experiments showed increased stress tolerance in the Agrobacterium-mediated transgenic
20
tall fescues through greenhouse/growth chamber evaluations of the F0; however further
field testing will need to be done to properly evaluate the true stress tolerance of the
transgenic plants (Kim et al., 2010; Zhao et al., 2007). Evaluation of the stability of these
transformations as the transformed plants are integrated into traditional breeding
programs is an important characteristic that must be researched further (Meyer and
Watkins, 2003). The use of transgenic turfgrass species is also often accompanied by
several environmental considerations, including gene flow to weedy turfgrass relatives
and escape of the perennial transgenic plant into areas where it is not wanted (Johnson
and Riordan, 1999).
21
SUMMARY AND OBJECTIVES
Previous studies have evaluated and compared diverse tall fescue cultivars during
drought stress, but not during heat and heat + drought stress (Carrow and Duncan, 2003;
Huang et al., 1998; Huang and Fry, 1998; Huang and Gao, 2000; Huang and Gao, 1999;
White et al., 1993; White et al., 1992). Additionally, individual cultivars of tall fescue,
perennial ryegrass, and Kentucky bluegrass have been evaluated under heat, drought, or
heat + drought stress, though diversity within species has not been assessed (Jiang and
Huang, 2001a; Jiang and Huang, 2001b; Jiang and Huang, 2000). To date, evaluation of
diverse tall fescues under heat or drought stress alone, or in combination has not been
conducted. Furthermore, while heritability analyses of disease resistance (Bokmeyer et
al., 2009; Watkins et al., 2009), root mass (Bonos et al., 2004), and various forage traits
(Annicchiarico and Romani, 2005; Burton and Devane, 1953; Nguyen and Sleper, 1983)
have been conducted on tall fescue, heritability of summer stress tolerance has not yet
been evaluated. Further research is needed to gain a better understanding of the specific
effects of the heat and drought components of summer stress, and to assess the
heritability of summer stress tolerance in tall fescue.
The objectives of this thesis were to:
1. Evaluate diverse field selected tall fescue genotypes in growth chambers for
performance under heat and drought stress alone and in combination.
2. Evaluate the use of growth chambers and rainout shelter structures for use in
screening germ plasm for summer stress tolerance.
3. Estimate heritability characteristics of summer stress tolerance in tall fescue.
22
LITERATURE CITED
Annicchiarico, P. and M. Romani. 2005. Genetic variation, heritability, and genetic
correlations for forage quality and yield traits of Mediterranean tall fescue
germplasm. Plant Breeding. 124:99-101
Asay, K.H., R.V. Frakes, and R.C. Buckner. 1979. Historical development. In R.C.
Buckner and L.P. Bush Eds. Tall Fescue. Agron. Monogr. 20. ASA, CSSA, and
SSSA, Madison WI.
Baird, J.H., D. Kopecký, A.J. Lukaszewski, R.L. Green, J. Bartoš, and J. Doležel. 2012.
Genetic diversity of turf-type tall fescue using diversity arrays technology. Crop
Sci. 52:408-412.
Beard, J. B. 1989. Turfgrass water stress: Drought resistance components, physiological
mechanisms, and species –genotype, diversity. In Proc. Int. Turf Res. Conf., 6th,
Tokyo. 31 July-5 Aug. 1989.
Beard, J.B. 1973. Turfgrass: Science and Culture. Prentice Hall, Englewood Cliffs, NJ.
Biran, I., B. Bravdo, I. Bushkin-Harav, and E. Rawitz. 1981. Water consumption and
growth rate of 11 turfgrasses as affected by mowing height, irrigation frequency,
and soil moisture. Argon. J. 73:85-90.
Blum, A. 1985. Breeding crop varieties for stress environments. CRC Rev. Plant Sci.
2:199-238.
Bokmeyer, J.M., S.A. Bonos, W.A. Meyer. 2009. Broad-sense heritability and stability
analysis of brown patch resistance in tall fescue. Hort Sci 44(2):289-292.
Bokmeyer, J., W.A. Meyer, J.A. Murphy, S.A. Bonos, R.F. Bara, D.A. Smith, M.M.
Wilson, and W.K. Dickson. 2004. Performance of tall fescue cultivars and
selections in New Jersey turf trials. Rutgers Turfgrass Proc. 36:151-185.
Bonos, S.A., D. Rush, K. Hignight, and W.A. Meyer. 2004. Selection for deep root
production in tall fescue and perennial ryegrass. Crop Sci. 44:1770-1775.
Borin, M., M. Vianello, F. Morari, and G. Zanin. 2005. Effectiveness of buffer strips in
removing pollutants in runoff from a cultivated field in North-East Italy. Agr.
Ecosyst Environ. 105:101-114.
Bormann, F.H., D. Balmori, and G.T. Gaballe. 2001. Redesigning the American lawn: a
search for environmental harmony 2nd Edition. Yale University Press, New
Haven.
Bowman, D.C. and L. Macaulay. 1991. Comparative evapotranspiration rates of tall
fescue cultivars. Hort Sci. 26(2):122-123.
Brar, G.S. and A.J. Palazzo .1995. Tall and hard fescue responses to periodic soil water
deficits. J Agron & Crop Sci. 175:221-229.
23
Brede, D. 2000. Turfgrass maintenance reduction handbook: sports, lawns, and golf.
Sleeping Bear Press, Ann Arbor.
Bremer, D.J., K. Su, S.J. Keeley, and J.D. Fry. 2006. Performance in the transition zone
of two hybrid bluegrasses compared with Kentucky bluegrass and tall fescue.
Online. Applied Turfgrass Science.
Buckner, R.C., H.D. Hill, and P.B. Burrus Jr. 1961. Some characteristics of perennial and
annual ryegrass X tall fescue hybrids and of the amphidiploid progenies of annual
ryegrass X tall fescue. Crop Sci. 1(1):75-80.
Buckner, R.C., J.B. Powell, and R.V. Frakes. 1979. Historical development. In R.C.
Buckner and L.P. Bush Eds. Tall Fescue. Agron. Monogr. 20. ASA, CSSA, and
SSSA, Madison WI.
Buckner, R.C., G.T. Webster, P.B Burrus Jr., and L.P Bush. 1976. Cytological,
morphological, and agronomic characteristics of tall X giant fescue hybrids and
their amphiploid progenies. Crop Sci. 16:811-816.
Burton, G.W. 1969. Improving turfgrasses. p. 410-424. In A.A. Hanson, F.V. Juska
(eds.). Turfgrass Science: Agron. Monogr. 14. American Society of Agronomy,
Madison, WI.
Burton, G.W. and E.H. Devane. 1953. Estimating heritability in tall fescue (Festuca
arundinacea) from replicated clonal material. Agron. J. 45:478-481.
Burton, G.W., E.H. DeVane, and R.L. Carter. 1954. Root penetration distribution and
activity in southern grasses measured by yields, drought symptoms and 32P
uptake. Agron. J. 46:229-233.
Carrow, R.N. 1996. Drought avoidance characteristics of diverse tall fescue cultivars.
Crop Sci. 36:371-377.
Carrow, R.N. and R.R. Duncan. 2003. Improving drought resistance and persistence in
turf-type tall fescue. Crop Sci. 43:978-984.
Cowan, J.R. 1956. Tall fescue. Adv. Agron. 8:235-320.
Cui, L., J. Li, Y. Fan, S. Xu, and Z. Zhang. 2006. High temperature effects on
photosynthesis, PSII functionality and antioxidant activity of two Festuca
arundinacea cultivars with different heat susceptibility. Bot. Stud. 47:61-69.
De la Peña, R., and J. Hughes. 2007. Improving vegetable productivity in a variable and
changing climate. J. of SAT Agri. Res. 4(1):1-22.
Dhanda, S.S. and G.S. Sethi. 1998. Inheritance of excised-leaf water loss and relative
water content in bread wheat (Triticum aestivum). Euphytica. 104:39-47.
24
Diab, A.A., B. Teulat-Merah, D. This, N.Z. Ozturk, D. Benscher, M.E. Sorrells. 2004.
Identification of drought-inducible genes and differently expressed sequence tags
in barley. Theor. Appl. Genet. 109:1417-1425.
Dong, S. and R. Qu. 2005. High efficiency transformation of tall fescue with
agrobacterium tumefaciens. Plant Sci. 168:1453-1458.
Duncan, R.R. and R.N. Carrow. 1997. Stress resistant turf-type tall fescue (Festuca
arundinacea Schreb.): Developing multiple abiotic stress tolerance. Int. Turf. Soc.
Res. J. 8:653-662.
Fu, J. and B. Huang. 2004. Leaf characteristics associated with drought resistance in tall
fescue cultivars. 1st IC on Turfgrass. (eds.) P.A. Nektarios. Acta Hort. 661.
Funk, C.R. and W.A. Meyer. 2001. 70 years of turfgrass improvement at the New Jersey
Agricultural Experiment Station Sept/Oct: 19-23.
Fry, J.D. and B. Huang. 2004. Applied Turfgrass Science and Physiology. John Wiley
and Sons, Hoboken, NJ.
Githinji L.J.M., J.H. Dane, and R.W. Walker. 2009. Water-use patterns of tall fescue and
hybrid bluegrass cultivars subjected to ET-based irrigation scheduling. Irrig Sci.
27:377-391.
Govindasamy, R., K. Sullivan, M. Brennan, V. Puduri, B. Clarke, and A. Adelaja. 2007.
The New Jersey turfgrass industry economic survey: Executive summary. Rutgers
New Jersey Agricultural Experiment Station: The Center for Turfgrass Science.
Hannaway, D.W., C. Daly, M. Halbleib, D. James, C.P. West, J.J. Volenec, D. Chapman,
X. Li, W. Cao, J. Shen, X. Shi, and S. Johnson. 2009. Development of suitability
maps with examples for the United States and China. In H.A. Fribourg, D.B.
Hannaway, and C.P. West (eds.) Tall Fescue for the Twenty-first Century. Agron.
Monogr. 53. ASA, CSSA, and SSSA, Madison, WI.
Hodges, A.W., J.J. Haydu, P.J. van Blokland, and A.P. Bell. 1994. Contribution of the
turfgrass industry to Florida’s economy, 1991-1992: a value-added approach.
University of Florida – Institute of Food and Agricultural Sciences.
Huang, B., J. Fry, and B. Wang. 1998. Water relations and canopy characteristics of tall
fescue cultivars during and after drought stress. Hort Sci. 33(5):837-840.
Huang, B. and H. Gao. 2000. Root physiological characteristic associated with drought
resistance in tall fescue. Crop Sci. 40:196-203.
Huang, B. and H. Gao. 1999. Physiological responses of diverse tall fescue cultivars with
drought stress. Hort Sci. 34(5):897-901.
Jauhar, P.P. 1975. Genetic regulation of diploid-like chromosome pairing in the
hexaploid species, Festuca arundinacea Schreb., and F. rubra L. (Graminae).
Chromosoma (Berl.) 52:363-383.
25
Jiang, Y. and B. Huang. 2001a. Drought and heat stress injury to two cool-season
turfgrasses in relation to antioxidant metabolism and lipid peroxidation. Crop Sci.
41:436-442.
Jiang, Y. and B. Huang. 2001b. Physiological responses to heat stress alone or in
combination with drought: A comparison between tall fescue and perennial
ryegrass. Hort Sci. 36(4):682-686.
Jiang, Y. and B. Huang. 2000. Effects of drought or heat stress alone and in combination
on Kentucky bluegrass. Crop Sci. 40:1358-1362.
Johnson, P.G. and T.P. Riordan. 1999. A review of issues pertaining to transgenic
turfgrasses. Hort Sci. 34(4):594-598.
Karcher, D.E., M.D. Richardson, K. Hignight, and D. Rush. 2008. Drought tolerance of
tall fescue populations selected for high root/shoot ratios and summer survival.
Crop Sci. 48:771-777.
Kim, K.-H., I. Alam, K.-W. Lee, S.A. Sharmin, S.Y. Lee, and B.-H. Lee. 2010. Enhanced
tolerance of transgenic tall fescue plants overexpressing 2-cys peroxiredoxin
against methyl viologen and heat stresses. Biotechnol. Lett. 32:571-576.
Kopec, D.M., R.C. Sherman, and T.P. Riordan. 1988. Evapotranspiration of tall fescue
turf. Hort Sci. 23:300-301.
Kramer, P.J. 1980. Drought, stress, and the origin of adaptations. In N.C. Turner and P.J.
Kramer (eds.). Adaptation of plants to water and high temperature stress. John
Wiley & Sons, New York.
Levitt, J. 1980. Responses of plants to environmental stresses 2nd edition volume 2.
Water, Radiation, Salt, and Other Stresses. Academic Press, NY.
Maricle, B.R., D.R. Cobos, and C.S. Campbell. 2007. Biophysical and morphological leaf
adaptations to drought and salinity in salt marsh grasses. Environ. Exp. Bot.
60:458-467.
Meyer, W.A., S.A. Bonos, K.A. Plumley, R.F. Bara, D.A. Smith, C.R. Funk, M.M. Mohr,
E. Watkins, J.A. Murphy, and W.K. Dickson. 2001. Progress in breeding for
disease resistance in open-pollinated cool-season turfgrasses. Proceedings of the
Tenth Annual Rutgers Turfgrass Symposium. pp. 22-23.
Meyer, W.A. and C.R. Funk. 1989. Progress and benefits to humanity from breeding
cool-season grasses for turf. p.31-48. In Sleper et al. (eds.) Contributions from
breeding forage and turfgrasses. CSSA Spec. Publ. 15. CSSA, Madison, WI.
Meyer, W.A. and E. Watkins. 2003. Tall Fescue (Festuca arundinacea). p. 107-127. In
M.D. Casler, and R.R. Duncan (eds.) Turfgrass Biology, Genetics, and Breeding.
John Wiley & Sons Inc. Hoboken, NJ.
26
Nguyen, H. T. and D. A. Sleper. 1983b. Genetic variability of seed yield and
reproductive characters in tall fescue. Crop Sci. 23:621-626.
Pallardy, S.G. and J.L. Rhoads. 1993. Morphological adaptations to drought in seedlings
of deciduous angiosperms. Can. J. Forest Res. 23(9):1766-1774.
Qian, Y.L., J.D. Fry, and W.S. Upham. 1997. Rooting and drought avoidance of warmseason turfgrasses and tall fescue in Kansas. Crop Sci. 37:905-910.
Rebetzke, G.J., R.A. Richards, A.G. Condon, and G.D. Farquhar. 2006. Inheritance of
carbon isotope discrimination in bread wheat (Triticum aestivum L.). Euphytica.
150:97-106.
Redmann, R.E., 1985. Adaptation of grasses to water stress: Leaf rolling and stomate
distribution. Ann. Missouri Bot. Garden. 72:833-842.
Robbins, P., T. Birkenholtz. 2003. Turfgrass revolution: measuring the expansion of the
American lawn. Land Use Policy. 20:181-194.
Saha, M., F. Kirigwi, K. Chekhovskiy, J. Black, and A. Hopkins. 2007. Molecular
mapping of QTLs associated with important forage traits in tall fescue. In T.
Yamada and G. Spangenberg (eds.) Molecular Breeding of Forage and Turf.
Saha, M.C., R. Mian, J.C. Zwonitzer, K. Chekhovskiy, and A.A. Hopkins. 2005. An
SSR- and AFLP-based genetic linkage map of tall fescue (Festuca arundinacea
Schreb.). Theor. Appl. Genet. 110:323-336.
Sleper, D.A. and J.M. Poehlman. 2006. Breeding Field Crops Fifth Edition. Blackwell
Publishing, Ames Ia.
Sheffer, K.M., J.H. Dunn, and D.D. Minner. 1987. Summer drought response and rooting
depth of three cool-season turfgrasses. Hort Sci. 22:296-297.
Sifers, S.I. and J.B. Beard. 1993. Comparative inter- and intra- specific leaf firing
resistance to supraoptimal air and soil temps in cool-season turfgrass genotypes.
p. 621-628. In R. N. Carrow, N.E. Christians, and C.C. Sherman (eds.)
Proceedings International Turfgrass Society Research Journal 7.
Sinclair, T.R., M.A. Zwieniecki, and N.M. Holbrook. 2007. Low leaf hydraulic
conductance associated with drought tolerance in soybean. Physiol. Plantarum.
134(4):446-451.
Sprague, H.B. 1982. Turf Management 3rd Edition. The Interstate Printers & Publishers
Inc., Danville, IL.
Sum K., D.J. Bremmer, and S.J. Keeley, J.D. Fry. 2007. Effects of high temperature and
drought on hybrid bluegrass compared with Kentucky bluegrass and tall fescue.
Crop Sci. 47:2152-2161.
27
Tiaz, L. and E. Zeiger. 2002. Plant Physiology: Third Edition. Sinauer Associates Inc.
Sunderland, MA.
Tredway, L.P., L. Butler, and J. Monroe. 2005. Managing brown patch in tall fescue
landscapes. Turfgrass Disease Info. Note 15. TURF-015. Plant Patho. Ext., North
Carolina State Univ., Raleigh.
Tuinstra, M.R., E.M. Grote, P.B. Goldsbrough, and G. Ejeta. 1997. Genetic analysis of
post-flowering drought tolerance and components of grain development in
Sorghum bicolor (L.) Moench. Mol. Breeding. 3:439-448.
Turgeon, A.J. 2005. Turfgrass Management 7th Edition. Prentice Hall, Upper Saddle
River N.J.
Wang, J.Z., L.J. Cui, Y. Wang, and J.L. Li. 2009. Growth, lipid peroxidation and
photosynthesis in two tall fescue cultivars differing in heat tolerance. Biol.
Plantarum. 53(2):237-242.
Wang, Z.Y., M. Scott, J. Bell, A. Hopkins, and D. Lehmann. 2003. Field performance of
transgenic tall fescue (Festuca arundinacea Schreb.) plants and their progenies.
Plant Sci. 173:501-509.
Watkins, E., S.A. Bonos, W.A. Meyer. 2009. Heritability of brown patch resistance in tall
fescue. International Turfgrass Science Research Journal. 11:271-281.
Werner, D.J. and T.L. Watschke. 1981. Heat tolerance of Kentucky bluegrasses,
perennial ryegrasses and annual bluegrass. Agron. J. 73:79-84.
White, R.H., A.H. Bruneau, and T.J. Cowett. 1993. Drought resistance of diverse tall
fescue cultivars. Int. Turf. Soc. Res. J. 7:607–613.
White, R.H., M.C. Engelke, S.J. Morton, B.A. Ruemmele. 1992. Competitive turgor
maintenance in tall fescue. Crop Sci. 32:251-256.
Wrigley, C.W., C. Blumenthal, P.W. Gras, and E.W.R. Barlow. 1994. Temperature
variation during grain filling and changes in wheat-grain quality. Aust. J. Plant
Physiol. 21:875-885.
Xu, S., J. Li, X. Zhang, H. Wei, and L. Cui. 2006. Effects of heat acclimation
pretreatment on changes of membrane lipid peroxidation, antioxidant metabolites,
and ultrastructure of chloroplasts in two cool-season turfgrass species under heat
stress. Environ. Exp. Bot. 56:274-285.
Zhao, J., W. Ren, D. Zhi, L. Wang, and G. Xia. 2007. Arabidopsis DREB1A/CBF3
bestowed transgenic tall fescue increased tolerance to drought stress. Plant Cell
Rep. 26:1521-1528.
Zhang, Y., M.A.R. Mian, and J.H. Bouton. 2006. Recent molecular and genomic studies
on stress tolerance of forage and turf grasses. Crop Sci. 46:497-511.
28
CHAPTER 2
Evaluation of Heat and Drought as Components
of Summer Stress on Tall Fescue Genotypes
ABSTRACT
Heat and drought are two major abiotic stresses causing a decline in quality in
cool-season turfgrasses during the summer. The objectives of this study were [1] to
determine whether heat stress or drought stress is the primary factor leading to the
summer decline of tall fescue in New Jersey and [2] to make selections of plants highly
tolerant to heat, drought, and/or heat + drought to be used in future breeding efforts.
Twenty-four tall fescue genotypes were selected from the germplasm pool present at the
New Jersey Agricultural Experiment Station (12 summer stress tolerant and 12 summer
stress sensitive).
Plants of these 24 genotypes were exposed to heat stress (38° C day/33° C night),
drought (by withholding irrigation), heat + drought (38° C day/33° C night with irrigation
withheld), or control (25° C day/20° C night and well-watered conditions). Declines in
turf quality (TQ), leaf photochemical efficiency (Fv/Fm), and leaf relative water content
(RWC) as well as an increase in electrolyte leakage (EL) occurred more rapidly in the
heat + drought treatment than in the heat or drought alone treatments. A decline in RWC
and an increase in EL occurred more rapidly in the drought treatment than in the heat
treatment. There were generally no significant differences in TQ, Fv/Fm, RWC, or EL
between summer stress tolerant and summer stress sensitive genotypes under drought or
heat + drought conditions. However, when comparing these two groups in the heat
treatment, plants selected as summer stress tolerant had significantly higher TQ, Fv/Fm,
29
RWC, and lower EL than those selected as summer stress sensitive. The results indicated
that the superior performance of the summer stress tolerant tall fescue in the field seems
to be mainly due to the superior heat tolerance.
30
INTRODUCTION
Cool-season turfgrasses exhibit a bimodal growth pattern, with most of their
growth and development in the spring and fall months and drastic decline in growth and
overall turf quality during the summer months (Turgeon, 2005). The decline in overall
turf quality of cool-season grasses during summer months is commonly referred to as
summer stress. Summer stress can be broken down into two major components, heat
stress, and drought stress (Jiang and Huang 2001b; Jiang and Huang, 2000; Huang et al.,
1998). While these two stresses often occur simultaneously, that is not always the case.
Quantification and comparison of the stress-induced decline caused by each will help
better combat the summer decline of cool-season turf grasses both through best
management practices (BMP) and breeding of improved varieties. The occurrence of
dormancy during periods of summer stress has been shown to be a desirable trait which
can aid in the long term survival of turfgrasses (Hopkins and Bhamidimarri, 2009;
Malinowski et al., 2005). However, for many turfgrass managers, dormant turf is not an
option; therefore, in this study dormancy will be considered a detrimental attribute.
Advancements made via breeding since the release of Kentucky 31 have
transformed tall fescue (Lolium arundinacea [Schreb.] Darbysh.) from a grass solely used
for minimally maintained utility applications into a viable option for areas of moderate
cultural intensity such as home and commercial lawns and athletic fields. This can be
attributed to new cultivars being finer textured, lower growing, and darker in color. Tall
fescue has long been considered one of the best cool-season grasses for heat and drought
tolerance (Turgeon 1980). While these high levels of tolerance to stresses were originally
31
made considering forage types such as Kentucky 31, newer turf type varieties still offer
levels of stress resistance as good as or better than the older cultivars (Carrow, 1996).
There are a number of ways that turf grasses are able to resist drought stress.
Carrow (1996) described two methods as (1) the ability to tolerate the dry down and
partial dehydration of cells, and (2) the ability to avoid drought by having a low level of
water use or by having a deep root system which provides a water source even during
periods of drought. Brar and Palazzo (1995) showed that tall fescues use considerably
more water with far more root biomass, even under drought conditions, than hard fescue
(Festuca brevilipa R. Tracey), another drought tolerant species. Tall fescue has also been
shown to have significantly higher water usage than many other common turfgrasses;
including chewings fescue (Festuca rubra L. sap comutata) , red fescue (Festuca rubra
L. rubra), hybrid Texas bluegrass (Poa pratensis L. x Poa arachnifera Torr.), perennial
ryegrass (Lolium perenne L.), St. Augustinegrass (Stenotaphrum secundatum [Walt.]
Kuntze), seashore paspalum (Paspalum vegitatum Swartz.), bermudagrass (Cydalon
dactylon L.), and hybrid zoysiagrass (Zoysia japonica x Z. pacifica), among others (Biran
et al., 1981; Githinji et al., 2009; Beard, 1989). Brar and Palazzo (1995) also reported that
while tall fescue uses more water, it has considerably more root biomass than hard
fescue. However, tall fescue’s drought avoidance mechanisms are more important to its
survival during drought than its drought tolerance mechanisms. The deep and expansive
root system is the most important aspect to its drought avoidance (Carrow 1996). In
addition to the deep roots of tall fescue being able to supply water to the plant to prevent
desiccation, this water loss can be used for transpirational cooling. Jiang and Huang
(2001b), compared tall fescue to perennial ryegrass, and showed that tall fescue had
32
higher leaf water content while experiencing heat and drought stress compared to
perennial ryegrass. They also suggested that tall fescue was cooling itself via
transpirational cooling and that this was one of the main factors leading to its superior
performance during heat and drought stress.
Global focus on environmental sustainability continues to spread and intensify
(Jiang and Huang 2001b). From 1960 to 2000, there have been increases of 30%, 28%,
24%, and 26% for each decade respectively in global water consumption (Kirda and
Kanber 1999). These steady increases have caused the worldwide consumption of
freshwater in 2000 to be up more than 160% from 1960 levels (Kirda and Kanber 1999).
As demand for the limited supply of fresh water continues to increase, it is likely that its
use for irrigation will become limited to food-crops, leaving turf managers with less
available water. Turfgrass managers at all levels are feeling the effects of this as they
continue to be pushed to decrease inputs while simultaneously maintaining the overall
esthetic and functional components of their turf. Turfgrass managers must be able to
pinpoint what is causing turf quality to decline in order to properly tailor best
management practices. The use of improved cultivars capable of maintaining quality
during periods of intense summer stress is another important tool. With this in mind, this
experiment was designed to [1] evaluate diverse tall fescues under heat and drought stress
alone and in combination, and [2] to select plants with a high level of summer stress
tolerance to be used in future breeding projects.
33
MATERIALS AND METHODS
Plant Material
Twenty-four experimental tall fescue genotypes with distinct summer
performance were selected from unirrigated space-plant nurseries consisting of over 5000
plants at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey. During
the summer of 2010, 24 genotypes were selected; 12 had 95-100% green tissue, and were
considered summer stress tolerant genotypes, and 12 had 0-5% green tissue, and were
considered summer stress sensitive. In order to prevent differences in turf performance
due to the presence or absence of endophytic fungi as described by Elbersen and West
(1996) and West (1994), all 24 genotypes were screened for the presence of endophyte
and all were found to be endophyte positive. Three vegetative replicates of each genotype
were transferred into plastic pots (10-cm-diameter x 36-cm-deep), filled with a mixture of
sterilized soil (fine-loamy-mixed mesic typic hapludult) and sand (2:1. v:v). Sixteen pots
of each of the 24 genotypes were made for a total of 384 pots.
Plants were grown for 50 days in a greenhouse with average daily temperatures of
25° C and a 14 h photoperiod. Ambient light was supplemented with 400-W high
pressure sodium lights (PL. Light Systems, Beamsville, Ontario, Canada) placed 1.5 m
above the plants. Plants were watered bi-weekly, or as soil drying was observed. A 16.03.5-5.0 water soluble quick release fertilizer was applied in two equal applications
immediately following, and 25 days after, transplanting in order to supply a total of 62.5
kg· hectare-1 (1.28 lbs./1000 ft2) of nitrogen.
Following plant establishment in the greenhouse, plants were moved to growth
chambers. The plants were allowed to acclimate to the chambers for 30 days prior to
34
treatments being imposed. During this acclimation period the chambers were set up to
provide a photoperiod of 14-h, photosynthetically active radiation of 500 μmol· m-2· s-1,
60% relative humidity, and day and nighttime temperatures of 25° C and 20° C,
respectively. The plants were hand trimmed two times each week to maintain a height of
7.5-cm. Heritage 0.8 TL (a.i. Azoxystrobin) was applied at a rate of 0.64-ml·m-2 seven
days prior to the start of the treatments and then again on day 15 in order to prevent
brown patch (Rhizoctonia solani) from infecting the plants.
The experiment was arranged in a randomized complete block design with four
replications. Four treatments were imposed: 1) well-watered control [C]: all plants were
watered as soil drying was observed, 2) heat stress [H]: all plants were watered to field
capacity as soil drying was observed and day and nighttime temperatures of 38° C and
33° C, respectively, 3) drought stress [D]: plants received no irrigation and day and
nighttime temperatures of 25° C and 20° C respectively, and 4) heat + drought stress
[H+D]: plants received no irrigation and day and nighttime temperatures of 38° C and
33° C, respectively. All other environmental conditions were the same in all four
treatments. Four chambers were used for this study. In order to mitigate chamber-related
variation, the plants and treatments were rotated between the chambers weekly.
Data Collection
Measurements of various shoot characteristics were made weekly on each plant
starting seven days after treatments were initiated. Treatments continued until a majority
of the plants receiving the treatment were dormant or until the end of the experiment on
35
day 30. Termination occurred on days 14 and 22 for the [H+D] and [D] treatments
respectively. Both the H and C treatments were maintained for the full 30 day period.
Turf quality (TQ) was a visual rating on a 1-9 scale of the overall performance of
the plant. This rating was based on that of Hays et al. (1991) with slight modifications, a
plant receiving a “9” was fully turgid, actively growing, and had no leaf browning or
firing; a plant receiving a “1” was completely wilted, not growing, complete leaf
browning, and was nearly dead or dormant.
Leaf photochemical efficiency was measured by using a fluorescence induction
monitor (Dynamax, Houston, TX) to measure the chlorophyll fluorescence of the leaf
tissue. Comparing the maximum fluorescence to the variable level at 690 nm can be used
to estimate the efficiency of photosystem II (Fv690nm/Fm690nm) (Krause and Weis,
1984; Zhang et al., 2003). Photosystem II is highly sensitive to heat stress and decreases
in efficiency as plants become heat stressed (Taiz and Zeiger, 2002)
Membrane stability was estimated by measuring leaf cell electrolyte leakage using
a variation of the methods described by Blum and Ebercon (1981) and Marcum (1998).
Approximately 1-g of leaf tissues were cut into 1-cm pieces. These leaf sections were
then rinsed with distilled deionized water. The leaf sections were placed into centrifuge
tubes containing 20 mL of distilled deionized water before being placed on shaker for 15
hours. After this initial incubation, the conductivity of the solution was measured (Model
32; Yellow Spring Instrument Co., Yellow Springs, OH) yielding the initial conductivity
(Ci). The tubes were then autoclaved for 30 minutes at 120° C in order to kill the plant
tissue. The tubes were allowed to cool and placed on a shaker for 15 hours. After the
second incubation, the conductivity of the solution was again measured, yielding the
36
maximum conductivity (Cmax). The electrolyte leakage was then calculated using the
equation: [%EL = (Ci)/(Cmax)·100].
Leaf relative water content (RWC), a percentage measure of the amount of water
in fresh leaves compared to the amount of water of the leaves when they are fully turgid,
was measured using the protocol described by Barrs and Weatherly (1962).
Approximately 0.3-g of fully-expanded leaf tissues were taken and weighed to obtain the
fresh weight (WF), the leaf tissue was then soaked in distilled water for 24 hours.
Following this incubation, the leaf tissue was removed from the water and any free
surface water was removed using a paper towel before they were weighed again, yielding
the turgid weight (WT). Following this weighing, the leaves were dried for 48 h in a
drying oven at 85° C before the dry weight (WD) was measured. The leaf RWC was then
calculated using the equation: [%RWC = {(WF)/(WD)}/{(WT)/ (WD )} ·100].
Volumetric soil water content (SWC) measurements were also taken weekly on
all plants at 20-cm depth using time-domain reflectometry (TDR) (Soil Moisture
Equipment, Santa Barbara, California).
37
RESULTS AND DISCUSSION
Summer stress tolerant genotypes did not exhibit significant differences from the
summer stress sensitive genotypes under [H+D], [D], or [C] treatment for any of the
parameters measured with one exception: turf quality was higher in summer stress
tolerant plants than summer stress sensitive plants under the [C] treatment. When
comparing these two groups in the heat stress treatment, summer stress tolerant
genotypes performed significantly better than those selected as summer stress sensitive in
TQ, Fv/Fm, RWC, and EL. (Fig. 2.1) The superior performance of the clones selected as
summer stress tolerant in only the heat stress chamber suggests that it is possible that the
superior performance of these clones in the field was a result of their high level of heat
tolerance.
Plants receiving the [H+D] treatment declined most rapidly in all measurements
(Tables 2.1, 2.2 and 2.3). These plants declined to the point that treatment had to be
stopped after 14 days because a majority of the plants had gone dormant and further
treatment would have likely lead to plant death. The plants receiving the drought
treatment deteriorated more quickly than the heat treated plants for photochemical
efficiency as well as electrolyte leakage (Table 2.3). These plants worsened to a level at
which a majority of them were dormant after 22 days and at this point the treatment was
stopped in order to prevent complete death. When comparing the deterioration of the
plants receiving the different treatments the decline for all measurements taken was
similar, with the decline being most rapid for the [H+D] treated plants, followed by the
plants receiving either the drought or heat treatment. These results supported the findings
of Jiang and Huang (2001b; 2000) in that [H+D] cause a more rapid overall decline than
38
either of the stresses alone. The decrease in average relative water content and increase in
average electrolyte leakage were significantly more rapid in the drought treatment
compared to the heat treatment. This is congruent with the findings of Jiang and Huang
(2001a) that tall fescue had a more rapid drop in relative water content under drought
stress than under heat stress. In this study, there was a significantly more rapid decline in
the relative water content of plants subjected to drought stress alone, when compared to
plants receiving the heat treatment. Various factors likely led to the rapid decline of the
drought treated plants in this study, including limited rooting depth, low relative
humidity, and constant airflow, among others. Restriction of rooting can have large
effects on the survival of tall fescue during drought stress (Carrow 1996; Huang and Gao,
2000).
There was a great deal of variation in overall performance of clones within
treatments, as well as the performance of single clones between treatments, this variation
is consistent with the diversity of tall fescues shown by Carrow (1996). Clone TF-8,
which was a top performing clone in the drought and the heat+drought treatment, was
one of the worst performing clones in heat stress treatment. While being the top
performing clone in the [D] and the [H+D] treatments, TF-8 also had the highest
volumetric soil water content in the final rating date for each of these treatments at 4.30%
and 4.75% respectively. These readings are significantly higher than the average of all
other clones at these two dates which were 3.25% in the [D] treatment and 3.21% in the
[H+D] treated plants based on LSD P=0.05. This suggests that clone TF-8’s superior
performance in these two treatments is a result of its low water usage. Further evidence to
support this hypothesis is evident from the observation of the performance of TF-8 in the
39
[H] treatment. In the [H] treatment, where TF-8 was one of the lowest performing clones,
it had very high soil moisture ratings. On the final rating date of the heat treatment, TF-8
had soil volumetric water content of 23.38%. This was significantly higher than the
average for all other plants which was 16.80%, based on LSD P=0.05. In this study, all
plants receiving a particular treatment were irrigated when a majority of the pots in that
treatment had noticeable soil surface drying. It is likely that TF-8 suffered detrimental
effects of having too much water, which can be significantly more detrimental when it
occurs in conjunction with high temperatures (Huang et al., 1998). The converse of TF-8
is TF-3. TF-3 was one of the top performing clones in the [H] treatment but was near the
bottom in the [D] and [H+D] treatments (Tables 2.1, 2.2, and 2.3). It had one of the
lowest volumetric soil water content of any clone in the [C], [H], [D], and [H+D]
treatments on their final measurement days. It is likely that TF-3 had high water usage.
This supports the findings of Jiang and Huang (2001b) that plants with higher water
usage can perform better in high heat because of high levels of transpirational cooling.
This is also consistent with the findings of Bowman and Macaulay (1991) that showed
significant intraspecific variation in the water usage of numerous tall fescue cultivars.
Intraspecific variation in water use has also been shown to occur in Kentucky bluegrass
(Ebdon et al., 1998)
TF-8 was selected as a summer stress sensitive clone under field conditions.
While it did perform well, as discussed earlier, in the [D] and [H+D] treatments, it is
suspected that this was a result of its low water use rate which meant it had availability
water for a longer period of time. This is consistent with the findings of Carrow (1996)
and Huang and Gao (2000) that deep root length density, which allows for a high
40
evapotranspiration rate, is more important to tall fescue’s overall resistance to summer
stress than having normally low water use rate. A low baseline evapotranspiration rate
has also been shown to not be a reliable indicator of overall drought tolerance; instead,
factors such as rooting depth are more important to the overall drought tolerance in other
species such as Kentucky bluegrass (Perdomo et al., 1996; Ebdon and Kopp, 2004). In
contrast, clone 3 was selected as summer stress tolerant under field conditions. This can
likely be attributed to the high level of heat tolerance that it exhibited in the field due to
its ability to transpire at high levels even during periods of drought because of a deep root
system as are found in various tall fescues (Huang and Gao, 2000)
TF-5, TF-6, and TF-10 were selected for performing well in one or multiple
chambers and therefore have been selected to be used in future breeding projects.TF-5
was selected for having the highest quality in the fourth week of the [H] treatment when
it rated a 7.8. TF-6 was selected for performing well in the [D] and [H+D] treatment
where it received a 7.8 and 7.3 quality rating respectively in their final rating dates. While
TF-10 did not perform extremely well in any of the treatments, it was selected for its
consistent, above average final quality ratings of 7.3, 5.3, and 6.0 in the [H], [D], and
[H+D] treatments, respectively.
Correlation analyses between turf quality and electrolyte leakage, relative water
content, and photochemical efficiency were performed on all clones in the [H], [D], and
[H+D] treatments. Electrolyte leakage, relative water content and photochemical
efficiency each correlated well with turf quality ratings in each of the three treatments.
Relative water content had the strongest correlation with turf quality ratings in the [H],
[D], and [H+D] treatments with r-values of r = 0.87, r = 0.76, and r = 0.73, respectively.
41
The weakest correlations with turf quality observed in each chamber were with
electrolyte leakage in the [H] and [H+D] treatment and photochemical efficiency in the
[D] treatment with r-values of r = -0.75, r = -0.52, and r = 0.62, respectively.
42
CONCLUSIONS
The summer decline of tall fescue plants during the hot dry summer of 2010 in
Adelphia, New Jersey was likely significantly affected by high temperatures. Plants that
were able to survive that summer were likely able to do so because of a higher level of
heat tolerance than others that went dormant or died. The fact that the plants selected as
summer stress tolerant did not perform significantly better in the drought and
heat+drought treatments is likely an artifact of this experiment being performed ex-situ in
growth chambers where it is impossible to truly match in-situ field conditions. Turf
managers should consider syringing as opposed to deep irrigation as an option for
combating summer stress. This can preserve the turf quality of heat stressed turfs without
using large amounts of water. The poor performance of TF-8 in the heat treatment was
most likely due to its becoming overwatered as a result of it comparatively low water
usage. TF-3 and TF-8 must be further tested in order to properly evaluate their summer
stress tolerance and characterize the strengths and weaknesses of both. TF-5, TF-6, and
TF-10 have been selected to be used for future summer stress tolerance breeding projects
that will work to provide turf managers with turfgrasses that are able to provide a high
level of overall turf quality during summer months without requiring a supplemental
irrigation.
43
LITERATURE CITED
Barrs, H.D. and P.E. Weatherley. 1962. A reexamination of the relative turgidity
techniques for estimating water deficits in leaves. Aust. J. Biol. Sci. 15:413–428.
Beard, J.B. 1989. Turfgrass water stress: drought resistance components, physiological
mechanisms, and species-genotype diversity. Keynote address, International
Turfgrass Research Conference, Tokyo, July 31-Aug 6.
Biran, I., B. Bravdo, I. Bishkin-Harav, E. Rawitz. 1981. Water consumption and growth
rate of 11 turfgrasses as affected by mowing height, irrigation frequency, and soil
moisture. Agron J 72:89-90.
Blum, A. and A. Ebercon. 1981. Cell membrane stability as a measurement of drought
and heat tolerance in wheat. Crop Sci. 21:43–47.
Bowman, D.C. and L. Macaulay. 1991. Comparative evapotranspiration rates of tall
fescue cultivars. Hort Sci 26(2):122-123.
Brar, G.S. and A.J. Palazzo .1995. Tall and hard fescue responses to periodic soil water
deficits. J Agron & Crop Sci 175:221-229.
Carrow, R.N. 1996. Drought avoidance characteristics of diverse tall fescue cultivars.
Crop Sci 36:371-377.
Ebdon, J.S. and K.L. Kopp. 2004. Relationships between water use efficiency, carbon
isotope discrimination, and turf performance in genotypes of Kentucky bluegrass
during drought. Crop Sci 44:1754-1762.
Ebdon, J.S., A.M. Petrovic, R.W. Zobel. 1998. Stability of evapotranspiration rates in
Kentucky bluegrass cultivars across low and high evaporative environments. Crop
Sci 38(1):135-142.
Elbersen, H.W. and C.P. West. 1996. Growth and water relations of field-grown tall
fescue as influenced by drought and endophyte. Grass Forage Sci 51:333-342.
Githinji, L.J.M., J.H. Dane, R.W. Walker. 2009. Water-use patterns of tall fescue and
hybrid bluegrass cultivars subjected to ET-based irrigation scheduling. Irrig Sci
27:377-391.
Hays, K.L., J.F. Barber, M.P. Kenna, T.G. McCollum. 1991. Drought avoidance
mechanisms of selected bermudagrass genotypes. Hort Sci 26(2) 180-182.
Hopkins, A.A. and S. Bhamidimarri. 2009. Breeding summer-dormant grasses for the
United States. Crop Sci 49:2359-2362.
Huang B., J. Fry, B. Wang. 1998. Water relations and canopy characteristics of tall
fescue cultivars during and after drought stress. Hort. Sci. 33(5):837-840.
Huang B. and H. Gao. 2000. Root physiological characteristics associated with drought
resistance in tall fescue cultivars. Crop Sci 40:196-203.
44
Huang, B., X. Liu, J.D. Fry. 1998. Shoot physiological responses of two bentgrass
cultivars to high temperature and poor soil aeration 38(5):1219-1224.
Jiang, Y. and B. Huang. 2001a. Drought and heat stress injury to two cool-season
turfgrasses in relation to antioxidant metabolism and lipid peroxidation. Crop Sci
41:436-442.
Jiang, Y. and B. Huang. 2001b. Physiological responses to heat stress alone or in
combination with drought: a comparison between tall fescue and perennial
ryegrass. Hort Sci 36(4):682-686.
Jiang, Y., B. Huang. 2000. Effects of drought or heat stress alone and in combination of
Kentucky bluegrass. Crop Sci 40:1358-1362.
Kirda, C., R. Kanber. 1999. Water, no longer a plentiful resource, should be used
sparingly in irrigation agriculture. In. C. Kirda, P. Moutonnet, C. Hera, and D.R.
Nielsen (eds.) Crop Yield Responses to Deficit Irrigation. Kluwer, Dordrcht.
Krause, H.G., E. Weis. 1984. Chlorophyll fluorescence as a tool in plant physiology. II.
Interpretation of fluorescence signals. Photo Res 5:139-157.
Marcum, K.B. 1998. Cell membrane thermostability and whole-plant heat tolerance of
Kentucky bluegrass. Crop Sci. 38:1214–1218.
Malinowski, D.P., H. Zuo, B.A. Kramp, J.P. Muir, W.E. Pinchak. 2005. Obligatory
summer-dormant cool-season perennial grasses for semiarid environments of the
southern great plains. Agron J 97:147-154.
Perdomo, P., J.A. Murphy, G.A. Berkowitz. 1996. Physiological changes associated with
performance of Kentucky bluegrass cultivars during summer stress. Hort. Sci.
31(7):1182-1186.
Taiz, L. and E. Zeiger. 2002. Plant physiology. Sunderland, MD: Sinauer Associates.
Turgeon, A.J. 2005. Turfgrass management. Upper Saddle River, NJ: Prentice Hall.
Turgeon, A.J. 1980. Turfgrass management. Reston, VA: Reston Pub.
West, C.P. 1994. Physiology and drought tolerance of endophyte infected grasses. Boca
Raton, FL: CRC Press.
Zhang X., E.H. Ervin, R.E. Schmidt. 2003. Plant growth regulators can enhance the
recovery of Kentucky bluegrass sod from heat injury. 43:952-956
45
Table 2.1. Quality ratings (1-9 visual ratings scale) of tall fescue genotypes evaluated
under heat, drought, heat and drought and control treatments in a growth chamber. Field
rating signifies plants selected under field conditions as summer stress tolerant (T) or
summer stress sensitive (S).
Field
Clone
Rating
Control
Heat
Drought
Heat+Drought
Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 1 Week 2
T
3
8.0
8.8
8.3
7.5
8.0
7.8
7.0
7.5
8.3
4.8
4.0
5.0
2.3
T
5
8.5
9.0
9.0
8.0
8.3
7.8
7.3
7.8
8.8
5.8
5.0
8.3
3.8
T
6
6.5
8.0
8.3
8.0
6.8
6.8
6.3
6.5
6.8
8.5
7.8
8.0
7.3
T
7
7.8
9.0
8.0
8.5
8.0
7.8
7.5
7.3
7.8
5.8
4.3
6.5
2.8
T
9
8.3
8.8
8.0
7.5
6.5
5.8
5.3
6.5
6.8
4.5
3.5
5.3
2.3
T
10
7.5
8.8
8.5
8.8
7.5
7.0
6.5
7.3
7.8
7.0
5.3
8.3
6.0
T
11
7.3
7.5
8.0
7.0
7.8
6.5
6.0
6.5
7.3
4.0
2.8
3.8
1.0
T
12
6.8
8.8
9.0
9.0
8.5
8.0
7.3
6.8
6.8
6.5
6.5
9.0
5.3
T
14
8.5
9.0
8.5
8.5
8.8
8.0
7.0
7.3
7.8
4.8
4.0
7.5
3.5
T
16
6.5
7.8
7.8
7.5
7.0
6.3
5.5
6.8
8.0
7.3
6.3
8.8
4.8
T
17
5.8
7.5
6.5
6.3
7.3
7.5
6.8
6.3
7.0
5.0
4.5
7.0
4.8
T
19
7.5
7.3
7.0
7.3
7.8
7.3
6.0
5.8
7.3
4.5
3.8
4.8
2.8
S
1
6.3
6.8
6.5
7.0
4.8
3.5
1.3
1.3
6.8
4.8
3.8
6.8
4.8
S
2
6.0
7.5
7.0
7.0
7.8
7.0
6.5
6.8
7.5
5.0
4.0
4.8
3.0
S
4
8.0
8.3
7.8
7.3
7.3
7.0
4.5
4.5
8.5
5.8
5.5
6.8
4.5
S
8
5.3
6.3
7.0
7.5
6.3
3.3
1.0
1.3
6.5
7.5
7.8
8.0
8.5
S
13
7.0
7.8
8.3
7.8
7.8
7.3
6.3
7.3
8.0
5.0
4.5
5.8
4.5
S
15
7.8
8.0
7.3
7.5
7.5
6.0
6.0
6.0
8.8
5.5
3.3
6.5
3.8
S
18
6.8
7.3
7.0
6.3
8.8
6.8
6.5
7.5
6.0
3.5
2.3
4.3
1.3
S
20
7.3
8.5
7.0
7.0
7.8
8.3
7.0
6.5
8.0
5.0
4.5
6.0
3.0
S
21
6.3
7.3
7.0
6.8
6.3
5.8
4.8
4.5
6.3
4.8
3.5
6.0
4.0
S
22
6.5
7.3
6.5
6.8
7.5
6.5
5.3
5.0
6.5
6.5
5.8
7.3
4.8
S
23
4.8
6.0
5.8
6.0
4.3
2.8
1.5
2.0
6.8
6.0
6.0
7.5
5.0
S
24
6.3
7.0
7.3
7.0
5.8
4.5
3.3
3.0
6.3
5.8
6.3
6.8
5.3
1.09
0.88
0.83
0.95
1.44
1.63
1.73
1.75
1.50
1.63
2.01
1.95
2.48
LSD P=0.05
46
Table 2.2. Relative water content readings (% of water in leaves compared to fully turgid
leaves) of tall fescue genotypes evaluated under heat, drought, heat and drought and
control treatments in a growth chamber. Field rating signifies plants selected under field
conditions as summer stress tolerant (T) or summer stress sensitive (S).
Control
Heat
Drought
Heat+Drought
Field
Rating
Clone
T
3
91.7
88.5
87.6
85.6
84.2
89.0
78.9
76.2
85.0
25.2
15.1
37.0
11.8
T
5
93.9
88.1
89.4
87.9
90.1
86.1
82.6
71.2
87.2
33.6
16.2
52.1
11.9
T
6
93.1
90.1
90.9
90.5
87.9
86.8
72.4
66.2
87.2
81.5
41.1
78.5
32.9
T
7
90.5
88.5
91.5
86.8
84.4
84.0
84.8
68.1
85.9
36.7
17.3
53.8
11.3
T
9
88.2
82.5
86.2
83.3
82.3
71.9
65.1
58.5
80.5
29.7
12.9
38.9
13.2
T
10
88.0
85.7
91.7
88.4
87.0
87.3
85.7
75.5
86.8
61.0
23.5
73.7
13.0
T
11
85.4
88.6
83.7
82.7
87.3
86.0
78.8
64.6
75.7
14.7
10.1
24.7
9.8
T
12
91.9
89.3
87.3
88.6
91.3
88.5
82.1
65.5
87.7
60.5
22.6
72.4
25.1
T
14
90.1
86.6
89.7
90.5
87.3
82.8
86.2
74.2
79.9
35.8
15.7
47.7
12.4
T
16
89.4
87.4
89.6
77.4
86.1
85.0
79.1
72.6
73.0
67.1
22.5
69.9
18.1
T
17
94.6
88.3
92.8
87.5
86.8
87.7
87.9
71.6
84.3
49.7
22.3
56.6
14.9
T
19
89.0
85.4
85.7
85.7
83.9
80.0
81.1
66.5
75.1
32.1
13.1
41.9
15.8
S
1
86.1
86.1
89.8
78.4
78.5
42.1
24.5
24.4
82.2
46.9
18.4
58.0
26.9
S
2
95.1
87.1
90.8
80.9
88.2
83.3
85.9
78.8
85.8
41.4
18.8
41.1
15.4
S
4
93.8
91.3
90.3
89.7
91.2
76.6
65.7
56.1
89.1
60.9
25.3
60.1
16.1
S
8
93.0
83.7
92.6
84.2
74.4
38.1
23.6
19.9
76.8
73.5
56.8
85.5
52.0
S
13
89.3
87.3
85.9
85.0
82.9
81.8
76.7
68.5
79.7
30.9
16.6
47.8
22.3
S
15
90.0
85.6
86.5
80.6
82.8
77.5
68.1
53.3
83.3
33.3
15.5
48.4
15.2
S
18
88.7
84.8
82.5
73.5
89.2
76.2
79.3
74.1
77.0
16.8
10.8
31.4
13.7
S
20
89.5
84.2
88.4
85.3
81.5
83.3
78.2
73.6
85.3
33.5
17.5
47.6
13.0
S
21
86.2
91.2
89.0
85.0
81.1
86.2
66.7
57.6
81.2
44.6
19.0
63.2
15.2
S
22
91.7
88.7
90.4
82.1
84.4
83.1
83.9
55.4
87.4
59.7
37.3
63.7
24.1
S
23
81.2
85.0
88.6
69.3
59.5
49.8
36.2
26.0
83.6
61.3
37.7
62.9
22.1
S
24
92.1
84.8
82.4
84.0
84.1
54.5
52.7
39.2
74.9
62.8
31.3
70.6
24.5
LSD P=0.05
7.62
6.56
6.67
9.71
9.51
13.75
16.03
22.04
13.84
15.64
12.71
19.16
12.68
Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 1 Week 2
47
Table 2.3. Electrolyte leakage readings (%) of tall fescue genotypes evaluated under heat,
drought, heat and drought and control treatments in a growth chamber. Field rating
signifies plants selected under field conditions as summer stress tolerant (T) or summer
stress sensitive (S).
Field
Clone
Rating
Control
Heat
Drought
Heat+Drought
Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 1 Week 2
T
3
52.1
57.0
53.7
64.0
57.4
56.5
58.7
59.5
37.9
72.3
93.7
47.6
81.8
T
5
60.0
55.3
49.7
51.7
53.6
58.8
53.4
53.2
35.9
54.4
93.9
29.7
81.4
T
6
58.2
54.9
57.6
49.4
52.1
63.6
70.5
65.8
42.3
57.7
67.6
21.2
64.9
T
7
55.7
52.6
62.0
50.4
56.9
52.7
56.4
57.7
40.7
68.0
85.8
39.1
82.6
T
9
55.8
62.4
52.3
51.8
68.4
66.4
71.6
96.5
41.4
69.1
89.8
33.0
82.9
T
10
52.5
59.9
55.9
46.9
58.0
62.2
69.4
61.0
35.4
57.1
83.9
25.2
86.9
T
11
57.0
58.3
58.4
51.9
60.4
64.3
64.3
62.2
39.9
84.0
98.4
69.3
83.3
T
12
52.0
49.7
51.8
48.9
54.0
55.1
58.5
54.6
34.5
52.8
71.3
22.9
72.2
T
14
57.6
50.0
52.8
45.4
60.9
50.5
58.7
55.1
39.9
68.4
93.5
29.6
86.0
T
16
57.4
55.2
61.9
58.5
56.2
63.9
69.1
59.6
42.0
56.0
89.4
27.8
83.7
T
17
50.8
46.6
49.5
51.4
59.2
55.6
58.2
60.0
38.6
58.8
81.1
21.9
77.5
T
19
52.5
59.6
58.8
50.5
52.8
67.5
64.8
60.6
41.8
70.5
94.2
46.4
83.0
S
1
56.4
61.6
62.9
61.6
64.4
89.1
98.8
98.0
49.6
56.5
89.0
32.9
77.5
S
2
57.4
53.9
58.4
61.1
55.7
61.7
62.1
55.8
37.3
72.2
91.8
45.4
83.3
S
4
56.1
55.1
51.9
44.6
49.9
61.5
68.7
76.6
35.4
52.5
72.0
33.3
77.8
S
8
51.0
55.8
46.9
55.1
57.3
93.6
99.1
97.7
43.2
53.7
68.2
31.7
61.8
S
13
50.8
51.9
53.0
56.9
58.2
68.2
71.3
52.1
36.8
89.3
88.3
37.1
78.4
S
15
58.2
59.9
61.3
62.9
66.4
67.8
65.8
69.0
48.5
65.2
93.8
44.0
84.0
S
18
60.5
64.5
63.1
62.5
63.2
65.1
59.4
60.1
39.5
77.5
98.5
51.2
79.1
S
20
52.9
54.3
58.5
57.7
61.4
59.3
55.5
56.1
37.9
65.8
89.1
34.6
85.8
S
21
58.5
59.6
66.0
60.2
60.8
73.0
73.6
83.7
45.1
69.8
95.0
28.7
87.9
S
22
50.9
52.2
55.1
49.6
54.7
57.3
58.3
70.5
42.2
53.0
79.3
22.5
72.6
S
23
56.5
61.8
62.1
75.6
60.7
92.6
93.8
93.7
43.1
62.6
83.1
35.3
74.5
S
24
57.3
58.1
60.5
52.0
65.8
74.2
79.3
86.5
46.9
62.5
84.6
26.9
76.5
9.19
10.82
7.71
9.44
11.46
11.02
13.51
21.35
17.62
19.30
10.66
16.28
9.53
LSD P=0.05
48
Figure 2.1. Turf quality (a), photochemical efficiency (b), relative water content (c)
and electrolyte leakage (d) of summer stress tolerant and sensitive tall fescue
genotypes evaluated under heat, drought, heat and drought and control treatments in a
growth chamber. Error bars indicate LSD values (P=0.05). The treatment and rating
week in which the data was taken are shown on the x-axis.
Turf Quality
Figure 2.1a
9
8
7
Summer
Stress
Sensitive
Quality
6
5
4
Summer
Stress
Tolerant
3
2
1
0
1
2
3
4
1
2
Control
3
4
1
Heat
2
3
Drought
1
2
Heat+Drought
Treatment and Week
Photochemical Efficiency
Figure 2.1b
0.9
Photochemical Efficiency
0.8
0.7
Summer
Stress
Sensitive
0.6
0.5
0.4
Summer
Stress
Tolerant
0.3
0.2
0.1
0
1
2
3
Control
4
1
2
3
4
1
Heat
Treatment and Week
2
Drought
3
1
2
Heat+Drought
49
Relative Water Content
Figure 2.1c
100
90
Relative Water Content (%)
80
Summer
Stress
Sensitive
70
60
50
40
Summer
Stress
Tolerant
30
20
10
0
1
2
3
4
1
2
Control
3
4
1
Heat
2
3
Drought
1
2
Heat+Drought
Treatment and Week
Electrolyte Leakage
Figure 2.1d
100
90
Electrolyte Leakage (%)
80
70
Summer
Stress
Sensitive
60
50
40
Summer
Stress
Tolerant
30
20
10
0
1
2
3
Control
4
1
2
3
4
1
Heat
Treatment and Week
2
Drought
3
1
2
Heat+Drought
50
CHAPTER 3
Field Testing of Summer Stress Tolerance in Tall Fescues
Using a Rainout Shelter Structure
ABSTRACT
Drought during summer months is a common problem for turfgrass managers.
Drought stress is exacerbated by high summertime temperatures. Many processes,
including root growth and photosynthesis, are extremely sensitive to high temperatures.
When these two stresses occur together, they are referred to as “summer stress”. The
objectives of this study were to [1] screen tall fescue germplasm to select plants with a
high level of summer stress tolerance which could be used in further breeding projects,
[2] evaluate the performance of tall fescue clones originally selected as summer stress
tolerant or summer stress sensitive, and [3] compare the performance of tall fescue clones
growing in a rainout shelter with their performance in the previously described growth
chamber study.
Twenty-four tall fescue genotypes, 12 summer stress tolerant and 12 summer
stress sensitive, were exposed to summer stress through the use of a rainout shelter
structure. The rainout shelter was constructed to close automatically, covering the test
area in the event of precipitation. Drought conditions were initiated through the use of
this structure in 2011 and 2012, with visual quality ratings being taken throughout each
stress period. Estimates of broad-sense heritability ranged from Hsp = 0.45 on a single
plant basis, to Hc = 0.77 when estimated on clonal means. There were significant
differences between the overall quality ratings of the summer stress tolerant and summer
stress sensitive groups, with the summer stress tolerant group having significantly higher
51
quality ratings on all but one rating date. Weak-moderate associations between quality
ratings in this study and the heat treatment in the previously described growth chamber
study were observed. High quality ratings in the rainout shelter study were associated
with high quality ratings in the heat stress growth chamber (r = 0.48).
52
INTRODUCTION
Global water usage rates increased over 160% through the past four decades of
the twentieth century, and it is estimated that the rate at which water usage has increased
will quicken (Kirda and Kanber 1999). Maintaining high quality turfgrass during summer
months can require large amounts of water. An average 18-hole golf course uses as much
as 1,000,000 gallons of water per day during hot and dry periods (Huck et al., 2000).
While golf courses and many other high value turfgrass areas often require supplemental
irrigation to maintain high turf quality, these areas will be some of the first to have
irrigation restricted as demand for water continues to increase for other more vital
operations (Kirda and Kandber, 1999; Milesi et at., 2005).
Compounding the issues of dry summers and irrigation restrictions, high
temperatures also cause a decline in quality of cool-season turfgrasses (Turgeon, 2005).
High air and soil temperatures both have significant detrimental effects on turfgrasses and
are considered the primary environmental factors responsible for the overall decline in
quality of cool-season grasses in the summer months (Fry and Huang, 2004). For coolseason turfgrasses, the optimal air temperatures for shoot growth are between 15° C and
24° C, and the optimal soil temperatures for root growth are between 10° C and 18° C
(Beard, 1973). While syringing, one of the only cultural practices available that can help
alleviate heat stress in turf grasses, can help prevent summertime heat induced damage, it
is a short term fix that requires water, and therefore cannot always be used (Turgeon,
2005). The combination of high temperatures and a lack of rainfall are commonly
referred to as “summer stress”.
53
The increasing demand for water is resulting in restrictions on irrigation of
turfgrasses during summer months. As these restrictions are becoming progressively
more common, managers must use species and cultivars genetically resistant to summer
stress. Of the cool-season turfgrass species, tall fescue (Lolium arundinacea [Schreb.]
Darbysh) has long been classified near the top with regards to drought resistance (Beard,
1973; Fry and Huang, 2004; Turgeon, 2005). Carrow (1996) asserted that performance
under dry conditions (drought resistance) was a result of a plant’s ability to tolerate
partial cell dehydration (drought tolerance), its ability to avoid drought (drought
avoidance), or a combination of the two. Drought avoidance can occur when plants either
have a low water use rate or have the ability to access water even during periods of
drought (Carrow, 1996). Tall fescue has been shown to have among the highest water use
rate of any turfgrass (Beard, 1989; Biran et al., 1981; Brar and Palazzo, 2005; Githinji et
al., 2009). Instead of limiting water use, tall fescue’s “excellent” drought avoidance (Fry
and Huang, 2004) is a result of its ability to access water with its deep root system even
during extended periods of drought (Carrow 1996; Huang and Gao, 2000a; Sheffer et al.,
1987). Sheffer et al. (1987) found tall fescue to have more than 10% of its root mass
deeper than 36-cm. Further studies have found tall fescue to have roots below 80-cm (Fu
et al., 2007).
Tall fescue is also considered one of the most heat tolerant of all cool-season
turfgrasses (Beard, 1973; Fry and Huang, 2004; Turgeon, 2005). The expansive root
system and high water use rate of tall fescue are thought to be responsible for its high
heat tolerance as they allow tall fescue to rapidly cool itself through transpirational
cooling (Jiang and Huang, 2001).
54
Growth chambers have commonly been used for turfgrass experimentation and
have provided a great deal of information on a variety of topics. Limitations of
experiments conducted in growth chambers can, however, make further evaluation in real
world conditions important. The expansive and deep rooting nature of tall fescue makes
proper evaluation of its drought tolerance difficult in growth chamber experiments.
Rainout shelter structures attempt to provide a method for implementing drought
conditions in a more realistic field setting. Numerous studies have used moveable rainout
shelters to provide drought conditions to plants growing in the field (Feldhake et al.,
1997; Fu et al., 2007; Steinke and Chalmers, 2010; Jiang and Carrow, 2005).
The objectives of this study were to [1] screen tall fescue germplasm to select
plants with a high level of summer stress tolerance to be used in further breeding projects,
[2] evaluate the performance of tall fescue clones originally selected as summer stress
tolerant or summer stress sensitive, and [3] compare the performance of tall fescue clones
growing in a rainout shelter with their performance in the previously described growth
chamber study.
55
MATERIALS AND METHODS
Plant Material
Twenty-four experimental tall fescue genotypes with distinct summer
performance were selected from unirrigated space-plant nurseries consisting of over 5000
plants at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey. During
the summer of 2010, the 24 genotypes were selected; 12 had 95-100% green tissue, and
were classified as summer stress tolerant, and 12 had 0-5% green tissue, and were
classified as summer stress sensitive. The 24 genotypes used in this study were clonal
propagates from the same plants selected for use in the previously described growth
chamber study. In order to prevent differences in turf performance due to the presence or
absence of endophytic fungi as described by Elberson and West (1996) and West (1994),
all 24 genotypes were screened for the presence of endphyte and all were found to be
endophyte positive. Clones were grown in a greenhouse during the winter of 2010.
Field Trial
In April of 2011, each clone was divided into four replicates, each containing
three tillers. Replicates were grown for one month in the greenhouse before they were
moved outside and allowed to grow for an additional month. On June 6, 2011, the clones
were planted in a randomized complete block design, with four replications, at the
Rutgers Agricultural Experiment Station in Adelphia, NJ. The soil type was a Freehold
sandy loam soil made up of 54% sand, 29% silt, and 17% clay. Each of the four replicates
contained one of each of 24 clones randomized among other experimental material.
Plants were spaced 31-cm apart and a border row was placed around the perimeter of the
field in order to provide uniform root competition. On June 8 and June 28, 3.66-g N·m-2
56
was applied using 19.0-0-5.0 (N-P-K) fertilizer. On June 13, Subdue (metalaxyl) was
applied at 4.58-g of product·m-2 to prevent pythium blight (Pythium spp). The planting
was done in an area that could be automatically covered by a double walled, air inflated,
plastic rainout shelter. Throughout establishment, the rainout shelter was deactivated and
remained open. Supplemental irrigation was applied as needed to facilitate establishment.
On August 2, 2011, the rainout shelter was activated, meaning that during rain events it
would close and prevent precipitation from reaching the plants.
On August 14, 26, and 27, the rainout shelter failed to close during periods of
heavy rain because of power failure. The rainfall totals for those three days were 7.3-cm,
9.5-cm, and 3.8-cm, respectively. Following the rainfall event on August 27, 2011, the
rainout shelter functioned properly for the remainder of the study. Quality ratings of each
plant were taken throughout the drought period as deterioration in quality became
apparent. Ratings were on a 1 to 9 scale, with 1 being a completely wilted or dormant
plant, and 9 being a green, fully turgid, actively growing plant. Texture ratings, on a 1 to
9 scale with 1 being a very coarse textured plant, and 9 being a fine textured plant, were
also taken at the beginning of the stress treatment. During 2011, the drought treatment
lasted from August 28 until November 8, when the rainout shelter was deactivated and
thorough irrigation was applied and a 10.0-4.4-8.3 (N-P-K) fertilizer was applied at a rate
of 3.66-g N·m-2, to allow plants to recover prior to winter.
In 2012, 3.66-g N·m-2 was applied using 10-4.4-8.3 (N-P-K) fertilizer and rainfall
was supplemented with irrigation as needed until April 19. Following 2.5-cm irrigation
on April 19, the rainout shelter was activated. Drought stress treatments were imposed
following the April 19 irrigation until August 7, when the plants were watered and
57
allowed to recover. During this period, quality ratings were taken throughout the stress
treatment, beginning when signs of drought stress were observed. Ratings of texture were
also made at the beginning of the treatment in both years. Volumetric soil water content
measurements were also taken during the stress period at 15-cm depth using time-domain
reflectometry (TDR) (Soil Moisture Equipment, Santa Barbara, California).
Statistical Analysis
Quality ratings were subjected to analysis of variance (ANOVA) using the PROC
ANOVA model in SAS (SAS Institute, Cary, NC). All quality data analysis was
conducted for the rating date from each year that exhibited the highest phenotypic
variance. In 2011, the third and final rating date on October 26, was used 2012 this was
the third rating date on June 25 was used. The summer stress conditions were so severe
following the 20 June rating date that ≈ 40% of plants received the lowest possible rating.
This resulted in limited variation among entries.
Broad-sense heritability was calculated based on clonal means (Hc) and on a
single plant (Hsp). Both estimates of broad-sense heritability were estimated using the
restricted maximum likelihood variance and covariance through the use of the PROC
MIXED model in SAS (SAS Institute, Cary, NC)(Bokmeyer et al., 2009; Bonos, 2006;
Bonos et al., 2004). Estimates of Hc and Hsp were calculated using the formulas: Hc =
σ2c/( σ2c+ σ2cy/y+σ2e/ry) and Hsp = σ2c/( σ2c+ σ2cy+ σ2e); where σ2c = genetic variance of
clones, σ2cy = clone x year variance, and σ2e = experimental error (clone x replication x
year) (Poehlman and Sleper, 1995).
Associations between various characteristics, including growth chamber
performance, rainout shelter performance, and leaf texture were determined using
58
correlation analysis (PROC CORR) (SAS Institute, Cary, NC). Correlation analysis were
performed on clonal means of all 24 clones used in this study. Clonal quality means in
the rainout shelter were the averages of the two-year performance of each genotype.
Clonal quality means in the heat growth chamber were the averages of each genotype on
the final rating date in each chamber.
59
RESULTS AND DISCUSSION
Following heavy rainfall events, substantial soil wetness was observed along the
edges of the rainout shelter. Soil wetness along the edges of the shelter was mainly due to
water being pulled into the dry experimental area from the adjacent moist soil due to the
more negative matric potential of the dry soil within the shelter. As a result, plants in the
outside row did not experience the same degree of drought stress and were disregarded
from all analyses.
Soil volumetric water content was measured in 2012 on June 14, July 13, and July
25 and showed averages of 13.5%, 12%, and 11.5%, respectively. Field capacity of this
soil was measured at ≈ 30% on June 14, by measuring soil outside of the rainout shelter
following a heavy rain event on June 13. Volumetric soil water content was fairly
uniform between replications. Differences in average quality ratings between reps were
generally small and not significant (Figure 3.1). The major exception to this was the July
13, 2012 rating. On the July 13, 2012, the quality average of plants in the first replication
was 3.0, significantly higher than the average quality or plants in each of the other three
replications, which were all 2.0. The higher quality average of the first replication could
be a result of increased airflow because of their placement in the open end of the rainout
shelter. The increase of airflow would have resulted in more efficient cooling of these
plants.
Analysis of variance showed clonal variability to be the largest component of the
variance (Table 3.1). The high percentage of overall variation in the population coming
from variability between clones points to summer stress tolerance being controlled
mainly by genetic factors. This analysis of variance was also used to estimate broad-sense
60
heritability on both a single plant and clonal average basis. The low broad-sense
heritability found on a single plant basis, Hsp = 0.45, only takes into account one
replication. When replications were factored in, broad sense heritably was estimated to be
Hc = 0.77. Burton and Devane (1953) had similar estimates of broad-sense heritability on
both a single plant and clonal average basis when evaluating forage characteristics in tall
fescues. These estimates ranged from 0.76 to 0.90 for 6-plant means, and from 0.34 to
0.59 for single plants (Burton and Devane, 1953). Comparable broad sense heritability
estimates (H2=0.64) have been calculated for performance under drought stress in
colonial bentgrass (Agrostis capillaris L.) x creeping bentgrass (Agrostis stolonifera L.)
hybrids (Merewitz et al., 2012). The large difference between these two estimates
suggests that environmental factors also contribute to the overall summer stress tolerance
of tall fescue. Additionally, these data suggest that multiple evaluations of the same clone
over several years are important for improving summer stress tolerance in tall fescue.
Clonal quality ratings had a normal, unimodal distribution in 2011 (Figure 3.2a).
The distribution of clonal performance became more spread out and less uniform in 2012
(Figure 3.2b). The separation that developed in the second year was expected since
clones were originally selected for being either summer stress tolerant or summer stress
sensitive. The separation of these two groups in the second year is displayed in Figure
3.3a and Figure 3.3b.
The 12 clones originally selected as summer stress tolerant had significantly
higher quality ratings than the clones selected as summer stress sensitive on all but one
date based on LSD P = 0.05 (Figures 3.4 and 3.5). In 2011, summer stress tolerant plants
had an average quality rating of 4.5, significantly higher than the summer stress sensitive
61
group that averaged 3.6. Similarly, the average quality of summer stress tolerant plants in
2012 was 4.3, which was significantly higher than the summer stress sensitive group at
2.9. The continuity of the overall performance of these two groups over multiple years
and multiple locations further strengthens earlier suggestions that drought tolerance in tall
fescue is a genetically controlled trait. These findings also suggest screening for summer
stress tolerance using a rainout shelter is a viable option. Clone TF-5 was found to
perform significantly better than all other clones tested, and as a result, was selected for
further evaluation and use in future breeding efforts (data not shown).
During the summer of 2012, the overall quality of clones declined steadily from
an average quality rating of 5.2 on May 16, to 1.4 on August 6 (Figure 3.6). The most
significant change came between the June 25 rating date, where the overall average was
3.6, and the July 11 rating when the average was 2.3. During the 15 day period between
these ratings, there was a period of 14 consecutive days where temperatures reached or
exceeded 30° C and 4 consecutive days where temperatures reached or exceeded 35° C.
Both of these were the longest such stretches during the summer of 2012. Prior to June
25, a total of 8 days had temperatures reaching or exceeding 30° C (Figure 3.6). These
sustained high temperatures are likely responsible for the large drop in overall quality
during this period. Root growth and maintenance is greatly affected by high temperatures.
Schmidt and Blaser (1967) showed 30% loss in root mass in creeping bentgrasses grown
at 36° C, compared to those grown at 24° C. The hypothesis that the rapid decline was a
result of these high temperatures is also reinforced by the findings of Huang and Gao
(2000b) that found at temperatures above 30° C, turf quality and root growth declined in
creeping bentgrass. Similarly, results have shown deterioration in quality and cessation of
62
growth of tall fescue caused by heat stress of 35° C (Wang et al., 2009). Wang et al.
(2009) also found significant differences in performance of tall fescues under heat stress.
The combination of high temperatures and lack of available water have been shown to be
more damaging to overall tall fescue turf quality than either stress alone (Jiang and
Huang, 2001).
During the 2011 drought treatment, temperatures were considerably lower. From
September 12, 2011 through October 24, 2011, the temperature only reached or exceeded
30° on three days, none of which were consecutive (Figure 3.7). These lower
temperatures, mainly within the optimal range for cool-season turfgrass growth, are likely
the cause of the increase in overall turf quality seen under drought stress during 2011.
Low fall temperatures are associated with root growth and recovery from summer stress
by numerous cool-season species (Huang and Gao, 2000b; Lyons et al., 2011)
No significant correlation was observed between texture and quality. Significant
correlation did exist between the heat growth chamber performance and rainout shelter
performance at P = 0.05. A moderate positive correlation (r = 0.48) existed between the
quality ratings in the heat chamber and quality ratings in the rainout shelter (Figure 3.8).
Significant correlations with relatively low r-values (as low as r = 0.41) were classified
as “moderate” correlations in previous breeding studies involving crested wheatgrass
[Agropyron cristatum (L.) Gaertn.] (Bushman et al., 2007; Hanks et al., 2005). The
correlation found in the current study, while weak, implies that 22.6% of the variation in
performance seen in the rainout shelter can be explained by the clonal performance in the
heat growth chamber. More generally, this correlation shows a positive association
between performance in the heat stress growth chamber and rainout shelter. Correlation
63
analyses were not performed between the rainout shelter and the drought or heat +
drought growth chamber treatments. Additionally, the overall lack of a strong correlation
between performance of clones in the rainout shelter and their performance in the growth
chamber further demonstrate the difficulty in accurately screening turfgrass germplasm
for summer stress tolerance in growth chambers.
64
CONCLUSIONS
This study indicates that summer stress tolerance in tall fescue is mainly
controlled by genetic factors, but that environmental variation also contributes to the
overall performance of tall fescue during summer months. Additionally, superior
performance of plants selected as summer stress tolerant while growing under field
conditions, compared to those selected as summer stress sensitive, suggests that the use
of rainout shelter structures for screening germplasm for summer stress tolerance is a
viable option.
A string of consecutive days with high temperatures above 30° C coincided with
the most rapid decrease in overall turf quality of plants growing in rainout shelter in
2012. When low soil moisture is coupled with these high temperatures, the severity of
stress inducted quality deterioration increases drastically. In much the same way, the
upward trend of quality ratings over time in 2011 suggest that cooler temperatures have
the ability to mitigate the effects of drought stress. These temperature data support earlier
conclusions that heat is the more detrimental component of summer stress in tall fescue.
Correlation between the performance of clones in the previously described growth
chamber experiment and their performance in this study suggest weak-moderate
associations exist; more specifically, associations between high quality ratings in the heat
stress growth chamber and high quality ratings in the rainout shelter. These findings
support the conclusions that drought resistance screening in a growth chamber can be
problematic and inaccurate.
65
LITERATURE CITED
Beard, J.B. 1973. Turfgrass: Science and culture. Prentice Hall, Englewood Cliffs, NJ.
Beard, J.B. 1989. Turfgrass water stress: drought resistance components, physiological
mechanisms, and species-genotype diversity. Keynote address, International
Turfgrass Research Conference, Tokyo, July 31-Aug 6.
Biran, I., B. Bravdo, I. Bushkin-Harav, E. Rawitz. 1981. Water consumption and growth
rate of 11 turfgrasses as affected by mowing height, irrigation frequency, and soil
moisture. Agron J 72:89-90.
Bokmeyer, J.M., S.A. Bonos, and W.A. Meyer. 2009. Inheritance characteristics of
brown patch resistance in tall fescue. Crop Sci. 49:2302-2308.
Bonos, S.A. 2006. Heritability of dollar spot resistance in creeping bentgrass.
Phytopathology. 96(8):808-812.
Bonos, S.A., C. Kubik, B.B. Clarke, and W.A. Meyer. 2004. Breeding perennial ryegrass
for resistance to gray leaf spot. Crop Sci. 44:575-580.
Brar, G.S. and A.J. Palazzo .1995. Tall and hard fescue responses to periodic soil water
deficits. J Agron & Crop Sci 175:221-229.
Burton, G.W. and E.H. Devane. 1953. Estimating heritability in tall fescue (Festuca
arundinacea) from replicated clonal material. Agron. J. 45:478-481.
Bushman, B. S., Waldron, B. L., Robins, J. G., and Jensen, K. B. 2007. Color and shoot
regrowth of turf-type crested wheatgrass managed under deficit irrigation. Online.
Applied Turfgrass Science doi:10.1094/ATS-2007-0418-01-RS.
Carrow, R.N. 1996. Drought avoidance characteristics of diverse tall fescue cultivars.
Crop Sci 36:371-377.
Elbersen H.W. and C.P. West. 1996. Growth and water relations of field-grown tall
fescue as influenced by drought and endophyte. Grass Forage Sci 51:333-342.
Feldhake, C.M., D.M. Glenn, W.M. Edwards, D.L. Peterson. 1997. Quantifying drought
for humid, temperate pastures using the crop water stress index (CWSI). New
Zeal. J. Agr. Res. 40(1):17-23.
Fu, J., J.D. Fry, B. Huang. 2007. Tall fescue rooting as affected by deficit irrigation. Hort
Sci. 42(3):688-691.
Fry, J.D. and B. Huang. 2004. Applied Turfgrass Science and Physiology. John Wiley
and Sons, Hoboken, NJ.
Githinji, L.J.M., J.H. Dane, R.W. Walker. 2009. Water-use patterns of tall fescue and
hybrid bluegrass cultivars subjected to ET-based irrigation scheduling. Irrig Sci
27:377-391.
66
Hanks, J.D., B.L. Waldron, P.G. Johnson, K.B. Jensen, K.H. Asay. 2005. Breeding
CWG-R crested wheatgrass for reduced-maintenance turf. Crop Sci. 45(2) 524528.
Huang, B. and H. Gao. 2000a. Root physiological characteristics associated with drought
resistance in tall fescue cultivars. Crop Sci 40:196-203.
Huang, B. and H. Gao. 2000b. Growth and carbohydrate metabolism of creeping
bentgrass cultivars in response to increasing temperatures. Crop Sci. 40:11151120.
Huck, M., R.N. Carrow, R.R. Duncan. 2000. Effluent water: Nightmare or dream come
true. USGA Green Selection Record. March/April. Pgs. 15-29.
Jiang, Y. and R.N. Carrow. 2005. Assessment of narrow-band canopy spectral reflectance
and turfgrass performance under drought stress. Hort Sci. 40(1):242-245.
Jiang, Y. and B. Huang. 2001. Physiological responses to heat stress alone or in
combination with drought: a comparison between tall fescue and perennial
ryegrass. Hort Sci 36(4):682-686.
Kirda, C., R. Kanber. 1999. Water, no longer a plentiful resource, should be used
sparingly in irrigation agriculture. In. C. Kirda, P. Moutonnet, C. Hera, and D.R.
Nielsen (eds.) Crop Yield Responses to Deficit Irrigation. Kluwer, Dordrcht.
Lyons, E.M., P.J. Landschoot, D.R. Huff. 2011. Root distribution and tiller densities of
creeping bentgrass cultivars and greens-type annual bluegrass cultivars in a
putting green.
Merewitz, E.B., F.C. Belanger, S.E Warnke, B. Huang. 2012. Identification of
quantitative trait loci linked to drought tolerance in colonial x creeping bentgrass
hybrid populations. Crop Sci. 52:1891-1901.
Milesi, C., S.W. Running, C.D. Elvidge, B.T. Tuttle, R.R. Nemani. 2005. Mapping and
modeling the biogeochemical cycling of turf grasses in the United States.
Environmental Management. 36(3):426-438.
Poehlman, J.M. and D.A. Sleper, 1995. Breeding field crops. Iowa State University Press.
Ames, IA.
Schmidt, R.E. and R.E. Blaser. 1967. Effects of temperature, light, and nitrogen on
growth and metabolism of ‘Cohansey’ bentgrass (Agrostis palustrus Huds.) Crop
Sci. 7:477-451.
Sheffer, K.M., J.H. Dunn, and D.D. Minner. 1987. Summer drought response and rooting
depth of three cool-season turfgrasses. Hort Sci. 22:296-297.
Steinke, K. and D. Chalmers. 2010. Refining qualitative turfgrass canopy stress
measurements during drought. Acta Hort. 881:451-456.
67
Turgeon, A.J. 2005. Turfgrass Management 7th Edition. Prentice Hall, Upper Saddle
River N.J.
Wang, J.Z., L.J. Cui, Y. Wang, and J.L. Li. 2009. Growth, lipid peroxidation and
photosynthesis in two tall fescue cultivars differing in heat tolerance. Biol.
Plantarum. 53(2):237-242.
West, C.P. 1994. Physiology and drought tolerance of endophyte infected grasses. Boca
Raton, FL: CRC Press.
68
Table 3.1. Analysis of variance of summer stress tolerance of 24 tall fescue clones
evaluated over 2 years (2011 and 2012) in a rainout shelter at the Rutgers
Agricultural Experiment Station in Adelphia, New Jersey.
Source of variation
Year
Rep
Clone
Clone*year
Error = clone*year*rep
df
1
3
23
23
121
Mean
Square
8.2158
2.0760
11.2120
2.7949
0.7678
F-value
10.7
2.7
14.6
3.64
Variance
P-value Component†
0.0467
0.0693
0.0000
1.0521
0.0000
0.5068
0.7678
Hc = 0.77
Hsp = 0.45
†
Variance components determined using restricted maximum likelihood (REML) of PROC Mixed
in SAS (SAS Institute, Cary, NC).
69
Figure 3.1. Comparison of visual quality ratings during the summer of 2012 between
replications of 24 tall fescue genotypes growing in a rainout shelter structure at the Rutgers
Agricultural Experiment Station in Adelphia, New Jersey. Error bars represent LSD at
P=0.05
6
Replication 1
5.5
Replication 2
Replication 3
5
Replication 4
4.5
Quality Rating
4
3.5
3
2.5
2
1.5
1
16-May
8-Jun
25-Jun
11-Jul
Rating Date
23-Jul
6-Aug
70
Figure 3.2. Clone quality distribution of tall fescue clones growing in a rainout shelter at the
Rutgers Agricultural Experiment Station in Adelphia, New Jersey on October 26, 2011 (a)
and June 25, 2012 (b).
30
(a)
Mean = 4.0
S.D. = 1.4
Number of Progeny
25
20
15
10
5
0
1
2
3
4
5
6
Quality Rating
7
8
9
30
(b)
Mean = 3.6
S.D. = 1.7
Number of Progeny
25
20
15
10
5
0
1
2
3
4
5
6
Quality Rating
7
8
9
71
Figure 3.3. Comparison of quality distributions of clones previously selected as summer
stress tolerant or sensitive. Quality ratings of plants growing in a rainout shelter at the
Rutgers Agricultural Experiment Station in Adelphia, New Jersey on October 26, 2011 (a)
and June 25, 2012 (b)
18
16
(a)
Summer Stress Sensitive
Mean = 3.6
Summer Stress Tolerant
Mean = 4.5
Number of Progeny
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Quality Rating
7
8
9
18
16
(b)
Summer Stress Sensitive
Mean = 2.9
Summer Stress Tolerant
Mean = 4.3
Number of Progeny
14
12
10
8
6
4
2
0
1
2
3
4
5
6
Quality Rating
7
8
9
72
Figure 3.4. Comparison of visual quality ratings over time during the summer of 2011
between clones selected as summer stress tolerant and summer stress sensitive at the
Rutgers Agricultural Experiment Station in Adelphia, New Jersey. Error bars represent LSD
at P=0.05.
6
5.5
5
4.5
Quality Rating
4
3.5
3
2.5
Summer Stress Tolerant
Summer Stress Sensitive
2
1.5
1
12-Sep
5-Oct
Date
26-Oct
73
Figure 3.5. Comparison of visual quality ratings over time during the summer of 2012 of tall
fescue clones selected as summer stress tolerant or summer stress sensitive growing in a
rainout shelter at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey. Error
bars represent LSD at P=0.05.
6
Summer Stress Tolerant
5.5
Summer Stress Sensitive
5
4.5
Quality Rating
4
3.5
3
2.5
2
1.5
1
16-May
8-Jun
25-Jun
11-Jul
Date
23-Jul
6-Aug
74
Figure 3.6. Daily atmospheric temperature ranges from May 16 – August 6, 2012 at the Rutgers Agricultural Experiment Station,
Adelphia, NJ. Average quality ratings of all plants growing the rainout shelter on each of the six rating dates are also shown.
40
6
35
5
25
4
20
3
15
Qualty Rating
Temperature in Degrees Celsius
30
10
2
Daily High Temperature
5
Daily Low Temperature
Overall Quality Average
0
16-May 23-May 30-May
1
6-Jun
13-Jun
20-Jun
27-Jun
Date
4-Jul
11-Jul
18-Jul
25-Jul
1-Aug
74
75
Figure 3.7. Daily atmospheric temperature ranges from September 1 - October 31, 2011 at the Rutgers Agricultural Experiment
Station, Adelphia, NJ. Average quality ratings of all plants growing the rainout shelter on each of the three rating dates are also shown.
40
6
35
30
25
4
20
3
15
Quality Rating
Temperature in Degrees Celsius
5
10
2
Daily High Temperature
Daily Low Temperature
Overall Qualty Average
5
0
1
1-Sep
8-Sep
15-Sep
22-Sep
29-Sep
Date
6-Oct
13-Oct
20-Oct
27-Oct
75
76
Figure 3.8. Rainout shelter-growth chamber correlation of clonal averages of 24 clones
grown in both a rainout shelter at the Rutgers Agricultural Experiment Station in
Adelphia, NJ and growth chamber heat stress treatment. Rainout shelter quality ratings
are averages for each clone over 2 years. Growth chamber quality ratings are averages for
each clone on the final rating date in the heat chamber.
Heat Growth Chamber Clonal Quality Average
9
(a)
8
7
6
5
4
3
y = 0.7276x + 2.9729
r = 0.48
2
1
1
2
3
4
5
6
Rainout Shelter Clonal Quality Average
7
8
9
77
CHAPTER 4
Inheritance of Summer Stress Tolerance in Tall Fescue
ABSTRACT
High summer temperatures, coupled with a lack of precipitation can lead to a
drastic deterioration in overall turf quality. Limited water supply and heavy restrictions
on its use in the turfgrass industry greatly limit the ability of turfgrass managers to
maintain cool-season turfgrasses during summer months. The objective of this study was
to evaluate the heritability of summer stress tolerance in tall fescue. Six distinct tall
fescue genotypes, three summer stress tolerant (TF-5, TF-6, and TF-10) and three
summer stress sensitive (TF-2, TF-15, and TF-21), were used as parents in a full diallel
cross and a polycross block. Progeny from these two populations, along with parental
clones, were evaluated in the field in a space-plant nursery located at the Rutgers
Agricultural Experiment Station in Adelphia, New Jersey. The field was unirrigated
during the summer of 2012 and visually rated for overall quality during a hot dry period
in the month of July. Estimates of narrow-sense heritability ranged from 0.66 for the
diallel cross population to 0.48 for the polycross population. Gains from selection of 52%
and 32% were estimated from the diallel and polycross populations, respectively, using a
5% selection intensity. Heterosis was present in 12 of the 30 diallel crosses suggesting
the presence of dominant and/or epistatic genes. The results of this study suggest that
additive gene action is a major component in the inheritance of summer stress tolerance
in tall fescue and that recurrent selection should be an effective breeding strategy for
improving summer stress tolerance in tall fescue.
78
INTRODUCTION
High temperature stress can be one of the most difficult stresses to manage
through cultural practices. Beard (1973) explained that aside from supplying water and
providing adequate airflow to allow for transpirational cooling, cultural practices for
controlling high temperature stress are limited to syringing. Syringing is a process in
which a small amount of water, typically around 0.6-cm , is applied to the turf canopy to
cool the turf and act as a heat sink to absorb heat and moderate heat accumulation (Beard
1973). Cultural techniques for handling drought stress of turfgrasses are straightforward
but come with their own set of difficulties and obstacles. During summer months, it is not
uncommon for an average 18-hole golf course to use as much as 1,000,000 gallons of
water in a single day (Huck et al., 2000). Although turfgrass occupies more than three
times the land of any other crop, it is not a food-crop, and thus will be the first to feel the
impacts of steadily increasing global water usage rates (Kirda and Kanber, 1999; Milesi
et al., 2005).
A lack of cultural techniques for alleviating heat stress in turf grasses, coupled
with increased demand for a limited water supply makes managing cool-season
turfgrasses during summer months increasingly more difficult. Genetically improved
turfgrasses are one of the best options for maintaining turf quality during summer
months. Tall fescue, traditionally one of the most summer stress tolerant of the coolseason turfgrasses (Beard, 1973) has shown great potential for use in a wide range of
turfgrass and forage applications in numerous environments (Friborugh et al., 2009).
Studies of the inheritance of increased heat and drought tolerance in agriculturally
important crops, including monocots have found it is a complex quantitatively inherited
79
trait (De la Peña and Hughes, 2007; Diab et al., 2004). Rebetzke et al. (2006) found
carbon isotope discrimination in bread wheat (Triticum aestivum L.), a trait previously
shown to be negatively correlated to transpirational efficiency, to be controlled primarily
by multiple additive genes. A high degree of additive gene action was also shown in
variations of excised leaf water loss rate and relative water content in wheat (Dhanda and
Sethi, 1998). Research on other monocots such as sorghum (Sorghum bicolor [L.]
Moench) has shown that various factors contributing to drought tolerance are each
controlled by multiple genes (Tuinstra et al., 1997).
Knowledge of the heritability characteristics of a trait of interest is important
when beginning a breeding program. Estimates of heritability can be used to select the
best breeding protocol, as well as anticipate gains that can be made (Nyquist, 1991).
Heritability is commonly expressed as broad-sense and narrow-sense heritability. Broadsense heritability is an estimate of the variance within a population caused by all genetic
factors (additive, dominance, and epistatic interactions) (Dudley and Moll, 1969).
Narrow- sense heritability is an estimate of the additive component of the total genetic
variance (Sleper and Poehlman, 2006). Burton and DeVane (1953) calculated estimates
of broad-sense heritability of various forage and seed yield characteristics of tall fescue.
While Burton and DeVane (1953) described the use of broad-sense heritability to
measure the potential efficiency of selection, estimates of narrow-sense have been shown
to be far more useful in breeding of out-crossing species (Nyquist, 1991).
In addition to estimations of heritability, other characteristics including heterosis,
maternal effects, and the approximate number of genes controlling a particular trait are
also important. Heterosis estimations are another tool plant breeders can use to gauge
80
whether dominant genes and epistasis are involved in a particular trait (Lynch and Walsh,
1998). The potential significance of epistasis in heterosis has been shown to be quite
significant in certain crops for specific traits. Yu et al. (1997), examined heterosis in rice
(Oryza sativa L.) yield and found “chain like” relationships present between loci of rice
in which locus A interacted with locus B, which then interacted with locus C, and so forth
to express a particular phenotype . These interactions were described as “multi-locus
epistasis”; where one locus could up/down regulate the expression of the second locus.
These chains could also act circularly to continually up/down regulate different loci they
contain. In addition to heterosis, maternal effects are also an important characteristic of
heritably. Understanding whether maternal effects are involved can also help breeders
understand whether progeny receive their genetic traits equally from both parents (Sleper
and Poehlman, 2006).
Diallel crosses are useful for plant breeders as they allow for calculations of many
heritably characteristics such as narrow-sense heritability, maternal effects, and heterosis
(Griffing 1956; Hayman, 1957; Sleper and Poehlman, 2006). These estimates can be used
to quantify how useful a specific parent can be in conferring traits to its progeny as well
as be used to compare the importance of additive vs. non-additive genes (Bokmeyer et
al., 2009; Sleper and Poehlman, 2006)
The objective of this study was to estimate narrow-sense heritability and evaluate
other characteristics of inheritance (maternal effects, minimum gene number, expected
gains from selection, and heterosis) of summer stress tolerance in tall fescue using a full
diallel cross and a polycross block between summer stress tolerant and summer stress
sensitive clones.
81
MATERIALS AND METHODS
Plant Material
Three summer stress tolerant (TF-5, TF-6, and TF-10) and three summer stress
sensitive (TF-2, TF-15, and TF-21) tall fescue clones were selected from the previously
described growth chamber study. Clones were originally screened as either summer stress
tolerant or summer stress sensitive while growing under field conditions after exposure to
severe summer stress. The Clones were further screened in a growth chamber for heat
and drought stress. Clones 5, 6, and 10 performed well both in the field and in the growth
chamber study, while clones 2, 15, and 21 performed poorly in both cases. In order to
prevent differences in turf performance due to the presence or absence of endophytic
fungi as described by Elbersen and West (1996) and West (1994), all 24 genotypes were
screened for the presence of endphyte and all were found to be endophyte positive The
six clones used in this study have significantly different pedigrees and are considered
unrelated.
Breeding
Diallel Cross
Crosses were made between clones in all possible combinations (tolerant x
tolerant, tolerant x sensitive, and sensitive x sensitive). Seed yield of all crosses was not
equal. A full description of crosses, including progeny yield, is shown in Table 4.1. Fullsib progeny were produced from each cross by using both clones as the female and male
parents. These full-sib F1 progeny were considered pseudo F2’s because the parents,
having never been inbred or test-crossed, were likely heterozygous at most loci (Fehr,
82
1987). Flower induction was encouraged by increasing day length to 14-hours using 400W high pressure sodium lights (PL. Light Systems, Beamsville, Ontario, Canada) placed
1.5 m above the plants in the greenhouse. Clones were either placed under, or removed
from the long day treatment depending on their particular maturity in order to
synchronize anthesis. Prior to anthesis, clones were matched with the desired cross and
crosses were isolated using plastic chambers. A waxed paper envelope was placed over
one seed head on each plant in order to measure the degree of selfing. No viable seed was
present in any of the seed heads that were placed in envelopes to test for selfing. Plant
inflorescences were manually tapped during anthesis to promote pollen movement
between clones
Seed from each clone was harvested separately, bagged, and dried in a
commercial seed dryer at 37° C for four weeks. Once dry, the seed was manually cleaned
and treated with 0.2% KNO3 in order to break dormancy and induce germination. After
the three day treatment in 0.2% KNO3, the seed from each cross was sown into a 20-cm
bulb pot and watered two times per day through germination. Following germination, 100
seedlings from both parents in each diallel cross were randomly selected and planted in
individual cells where they were allowed to grow for three months. One hundred
seedlings from each mother genotype in the polycross block were randomly selected and
planted in the same manner.
Polycross Block
Two clones of each of the six genotypes described above were used to create a
polycross block. Parental genotype TF-10 produced only 95 viable seeds while all other
genotypes produced more than the 96 used for evaluation in this experiment. A full
83
description of the polycross block is presented in Table 4.2. Flowering was induced as
described above. Clones used in the polycross block were arranged in a randomized
complete block design, isolated in a separate room from the diallel crosses, and rerandomized every second day in an attempt to limit assortative mating. Oscillating fans
were also used in addition to manual tapping to assist in pollen movement. Progeny from
the polycross block were half-siblings because the pollen source is considered the same
for the entire block (Nguyen and Sleper, 1983a). Polycross blocks are the most common
method of synthetic cultivar production in turfgrass breeding (Meyer and Watkins 2003).
Polycross isolation nurseries allow for random intermating between selected plants, fix
gene frequency in the population, and begin the process of seed increase (Vogel and
Pedersen, 1993). Seed harvest, processing, and plating was performed as described above
Field Planting and Evaluation
Progeny from both parents of each diallel cross, along with clonally propagated
parents were planted in the field in a randomized complete block design with four
replicates at the Rutgers Agricultural Experiment Station in Adelphia, NJ in October of
2011. Soil type was a Freehold sandy loam, made up of 69% sand, 21% silt, and 10%
clay. Each of the four replicates contained 24 progeny from each parent (when possible)
in the diallel cross as well as four clonal plants of each parent. Some crosses did not
produce enough viable seed to provide enough progeny to have 24 in each replication. In
instances where there were not 96 progeny, the available progeny were divided equally
among the 4 replicates. Plants were placed 31-cm apart. A border row was planted around
the perimeter of the field in order to provide more uniform root competition throughout
the experiment and alleviate an edge effect. Empty plots where there were not enough
84
progeny from a particular cross were also planted with border plants for the same reason.
Progeny from each maternal genotype of the polycross block, along with clonally
propagated parents were planted in an adjacent field using an identical method.
Immediately following planting, 10.0-4.4-8.3 (N-P-K) fertilizer was applied at a rate of
3.66-g N·m-2. Plants were maintained at 6.4-cm height during the growing season with a
rotary mower. Rainfall was supplemented with irrigation as needed following planting as
well as during the following spring to assure proper establishment.
In the spring of 2012, two fertilizer applications of 3.66-g N·m-2 each were
applied using a 19.0-0-5.0 (N-P-K) fertilizer on March 15 and April 12. Rainfall was
supplemented with irrigation until the month of June, at which point supplemental
irrigation was ceased. From June 26 through July 25, rainfall was not more than 0.8-cm
on any one day and totaled only 3.3 cm. During this period, the average daily high
temperature was 32° C and nine of the 30 days had highs reaching or exceeding 35° C.
Ratings of each plant were taken weekly on a 1 to 9 scale with 1 being a completely
wilted or dormant plant, and 9 being a green, fully turgid, actively growing plant. After
July 26, due to regular heavy rains, significant stress was not observed on the plants so no
further stress ratings were taken. Texture ratings were also taken on a 1 to 9 scale with 1
being a very coarse textured plant, and 9 being a fine textured plant. Volumetric soil
water content measurements were also taken during the stress period at 15-cm depth
using time-domain reflectometry (TDR) (Soil Moisture Equipment, Santa Barbara,
California).
85
Statistical Analysis
All quality data analysis was conducting using the final rating date when drought
stress was most severe and variance was greatest. Narrow-sense heritability was
estimated by performing a regression analysis of mid-parent and progeny means (Bonos,
2006; Sleper and Poehlman, 2006). In the diallel cross, means of progeny were regressed
against the mid-parent mean for each cross. The slope of the regression line is equal to
the narrow-sense heritability (Falconer and MacKay, 1996; Sleper and Poehlman, 2006).
Narrow-sense heritability was estimated the same way for the polycross block except that
the male parent was the average of all parents because of the assumed uniform pollen
pool (Nguyen and Sleper, 1983a).
Expected gain from selection was calculated using the formula GS= (i) (σp) (h2),
where GS is the expected gain from selection, i is the selection intensity, σp is the
phenotypic standard deviation of the entire population, and h2 is the narrow sense
heritability (Sleper and Poehlman, 2006).
Heterosis and maternal effects in the diallel cross were tested for significance
using a two-sample t-test. The presence of heterosis was determined by comparing
progeny and mid-parent means. Comparisons of progeny means of reciprocal crosses
were used to test for the presence of maternal effects (Fehr, 1987; Hartl and Jones, 2005;
Johnson and Bhattacharyya, 2007; Kitchens, 1998).
The minimum number of genes estimated to be involved with performance under
heat and drought was calculated using the equation described by Wright (1968). In this
equation, n = (P1-P2)2/8(σ2F2- σ2E), n is the minimum number of genes, P1 and P2 are the
86
parental ratings, σ2F2 is the variance of the progeny, and σ2E is the pooled variance of all
clonal parent lines.
87
RESULTS AND DISCUSSION
Severe summer stress conditions caused a significant deterioration in the overall
quality of tall fescue clones and progeny. While stress symptoms were present in all
plants evaluated by the final rating date, some only suffered minor reductions in overall
turf quality, while others became fully dormant or died. Both the diallel and polycross
population distributions were bell-shaped with a few plants at each extreme but a
majority of the plants performing directly in the middle of the two limits (Figure 4.1).
Significant differences existed between parental clones selected as summer stress tolerant
and those selected as summer stress sensitive in both the diallel population and the
polycross block population between clones. The average quality ratings of summer stress
tolerant parental clones were 5.1 and 4.3 in the diallel and polycross plantings,
respectively, both values were significantly higher than average quality rating of the
summer stress sensitive parents in the corresponding plantings of 3.8 and 2.8.
Significant differences between replications were present in both the diallel and
the polycross populations. In the diallel population, plants in replication one, two, and
three had average quality ratings of 4.2, 4.4, and 4.5, respectively, which were
significantly lower than the quality ratings of plants in the fourth replication of 5.0 on the
final rating date (Rep 1 = Rep 2 = Rep 3 < Rep 4) (P = 0.05). The difference in the
overall performance of plants in each rep can be explained by difference in soil moisture
in the field. The final average soil volumetric water content readings were 10.6%, 12.4%,
12.7%, and 13.7% in replications 1, 2, 3, and 4, respectively. In the polycross population,
average quality ratings of replications one (4.6) and two (4.6) were significantly lower
than the average ratings of replications three (5.4) and four (5.4) on the final rating date
88
(Rep 1 = Rep 2 < Rep 3 = Rep 4) (P = 0.05). Similar to the diallel cross, these differences
can likely be attributed to variation in soil moisture thought the field. Soil volumetric
water averages on the final rating date were 10.4%, 11.3%, 13.5% and 15.8%,
respectively. Soil volumetric water content declined from and overall average of 16.2%
on July 6, when significant stress was first visible, to 12.3% on July 25th, the final rating
date.
Narrow-sense heritability of summer stress tolerance was estimated separately for
the diallel and polycross populations. Both were estimated using mid-parent/progeny
regression analysis, with the slope of the regression line being the narrow-sense
heritability. Narrow-sense heritability values of 0.66 and 0.48 were estimated for the
diallel and polycross, respectively (Figure 4.2). Narrow sense heritability estimates the
effect of additive genes only, removing the effects of dominant genes and epistasis,
which are not as useful to plant breeders (Hartl and Jones, 2005). The narrow-sense
heritability estimated for the diallel cross is considerably higher than the estimate for the
polycross population. While the six-clone diallel cross had 30 different parent-progeny
combinations used in its regression analysis, the six-clone polycross had only six
different combinations due to the assumption of a uniform pollen source. As a result, the
regression analysis is far less powerful in the polycross where fewer points were plotted.
Other reasons for the lower narrow-sense heritability estimate in the polycross population
is the possibility of the occurrence of assortative mating.
Lehman and Engelke (1991) estimated the narrow sense heritability of root
growth, a trait associated with summer stress tolerance, in creeping bentgrass (Agrostis
stolonifera L.) to be between 0.62 and 0.72. Similar tall fescue narrow-sense heritability
89
estimates of 0.67 and 0.86 have been estimated for seed yield and maturity, respectively
(Nguyen and Sleper, 1983b). Ekanayake et al. (1985) had similar narrow-sense heritably
estimates for characteristics associated with drought resistance in rice. Narrow-sense
heritability was estimated to be 0.56-0.92 for dry root weight, 0.44-0.77 for root length
density, and 0.61-0.80 for root thickness (Ekanayake et al., 1985). The moderate-high
narrow-sense heritability estimated in the diallel population in this study points to
summer stress tolerance in tall fescue primarily controlled by a multiple additive genes.
The high proportion of additive genes involved with summer stress tolerance in tall
fescue, is similar to findings in other monocots (Ekanayke et al., 1985; Lehman and
Engelke, 1991)
Narrow-sense heritability estimates additionally can be used to estimate gain from
selection. Sample variance, along with narrow-sense heritability, was used to estimate
that a 52% gain would be achieved from a selection of the top 5% of the diallel
population. Selection of the top 5% of polycross population was estimated to result in a
32% gain. Bonos et al. (2004) estimated gain from a 2-4% selection intensity for root
mass below 30-cm for tall fescue, and similarly found expected gains to be 41% for a
genetically narrow population and 81% for a genetically diverse population. Burton and
Devane (1953) also calculated expected gain from selection of the top 5% of a population
of tall fescue growing as space-plants during the summer in Tifton, Georgia. Expected
gains in greenness ratings and yield of green tissue were estimated to be 39.4% and
60.5%, respectively (Burton and Devane, 1953).
The diallel population was further analyzed to determine additional characteristics
of heritably. Mid-parent means were significantly different from progeny means in 12 of
90
the 30 crosses, meaning that heterosis was present (Table 4.1). In four of the twelve
crosses displaying heterosis, it was negative, with the progeny performance being inferior
to that of the mid-parent. In the other eight crosses exhibiting heterosis, the progeny
performed better than the mid-parent. Additionally, all but one of the crosses exhibiting
significant heterosis involved clones TF-10, TF-15, or TF-21 as one or both of the
parents. The occurrence of heterosis in crosses can be caused by a number of factors
including the presence of dominant genes and/or epistatic interactions. Similarly, the
presence of negative and positive heterosis has been shown for various productivity
characteristics in rice (Huang et al., 2006; Xiong et al., 1998). Huang et al. (2006)
identified a phenomenon called “expression polymorphism” in which different
expression levels of identical genes were observed between different genotypes.
Expression polymorphisms were found on a large number of genes and were theorized to
be an explanation for the positive and negative heterosis observed in that study.
Expression polymorphisms were found in cases where both parents highly expressed the
gene but expression was low in the progeny, both parents had low expression but progeny
expression was high, and in cases where one parent had high expression and the other
parent and hybrid had low gene expression (Huang et al., 2006). Negative
heterosis/heterosis for susceptibility, has similarly been shown in creeping bentgrass with
relation to dollar spot resistance (Bonos, 2006).
Overall progeny performance in the diallel population (mean quality = 4.4) was
not significantly different from the overall parental performance (mean quality = 4.6). In
contrast, progeny in the polycross population (mean quality = 5.7) performed
significantly better than their parental clones (mean quality = 4.3). Non-uniform mating,
91
in which high performing clones produced more pollen could be a possible cause for this
difference in performance.
Estimation of the minimum number of genes involved was calculated to be as
high as 5.2 (Table 4.3). For one cross, 21 x 6, calculation of the minimum number of
genes involved resulted in a negative value of -0.8. It is likely that this, and many of the
other low values calculated for the minimum gene number, is the result of violating
assumptions on which the calculation is based. Some of the assumptions likely violated in
this instance are that both parents are inbreds, all genes have equal effect, there is no
linkage, and that all genes are additive (Sleper and Poehlman, 2006). Calculations of
heterosis suggest that non-additive gene action is present in some crosses. Heterosis, for
example, was significant in the cross that resulted in the negative gene number result. In
addition to the presence of non-additive gene action, it is also known that, due to the selfincompatibility of tall fescue, the parents are not inbreds. While this estimation of the
minimum number of genes involved with a quantitative trait can be useful, its limitations
should be noted.
Significant differences between progeny averages in reciprocal crosses were
observed in four of the thirty crosses (Table 4.3). These differences indicate the presences
of maternal effects. Two crosses exhibiting significant maternal effects were sensitive x
sensitive, one was sensitive x tolerant, and one was tolerant x tolerant. Of the four crosses
where significant maternal effects were present, three involved clone 21. These results
indicate that clone 21, when used as the female parent, had a negative effect on summer
stress tolerance. These findings are similar to those of Bonos et al. (2003) who found
maternal effects pertaining to disease resistance in creeping bentgrass related to the poor
92
performance of a particular genotype. The poor performance of progeny of crosses
involving clone 21 as a maternal parent also suggest the possibility of components of
summer stress tolerance or susceptibility being inherited through cytoplasmic genomes
(Roach and Wulff, 1987; Wright, 1968).
93
CONCLUSIONS
This study indicates that summer stress tolerance is mainly controlled by genetic
factors, and more specifically, additive gene action. The presence of heterosis in some of
the diallel crosses suggests the potential presence of dominant and/or epistatic gene
action; however, these interactions were only present in 40% of the diallel crosses. While
dominant and/or epistatic gene action may be present, it likely makes up only a small
proportion of the total genetic variation. These data as a whole indicate that summer
stress tolerance in tall fescue is controlled mainly by many additive genes and that
breeding programs involving recurrent selection and/or multiple cycles of progeny testing
would be successful in improving the overall summer stress tolerance of tall fescue.
Further evaluation of the parental clones and their progeny is an important next
step in the evaluation of these populations. So far, only one year’s data, in a single
location has been collected. The evaluation of both the diallel cross and polycross
populations over an additional year will provide more accurate estimations of various
heritability characteristics and components. Evaluations in future years can also be used
to determine to what degree the development of the plant over multiple years will affect
its summer stress tolerance.
94
LITERATURE CITED
Beard, J.B. 1973. Turfgrass: Science and culture. Prentice Hall, Englewood Cliffs, NJ.
Bokmeyer, J.M., S.A. Bonos, and W.A. Meyer. 2009. Inheritance characteristics of
brown patch resistance in tall fescue. Crop Sci. 49:2302-2308.
Bonos, S.A. 2006. Heritability of dollar spot resistance in creeping bentgrass.
Phytopathology. 96(8):808-812.
Bonos, S.A., M.D. Casler, and W.A. Meyer. 2003. Inheritance of dollar spot resistance in
creeping bentgrass. Crop Sci. 43:2189-2196.
Bonos, S.A., D. Rush, K. Hignight, and W.A. Meyer. 2004. Selection for deep root
production in tall fescue and perennial ryegrass. Crop Sci. 44:1770-1775.
Burton, G.W. and E.H. Devane. 1953. Estimating heritability in tall fescue (Festuca
arundinacea) from replicated clonal material. Agron J. 45:478-481.
De la Peña, R., and J. Hughes. 2007. Improving vegetable productivity in a variable and
changing climate. J. of SAT Agri. Res. 4(1):1-22.
Dhanda, S.S. and G.S. Sethi. 1998. Inheritance of excised-leaf water loss and relative
water content in bread wheat (Triticum aestivum). Euphytica. 104:39-47.
Diab, A.A., B. Teulat-Merah, D. This, N.Z. Ozturk, D. Benscher, M.E. Sorrells. 2004.
Identification of drought-inducible genes and differently expressed sequence tags
in barley. Theor. Appl. Genet. 109:1417-1425.
Dudley, J.W. and R.H. Moll. 1969. Interpretation and use of estimates of heritability and
genetic variance in plant breeding. Crop Sci. 9:257-262.
Elbersen H.W. and C.P. West. 1996. Growth and water relations of field-grown tall
fescue as influenced by drought and endophyte. Grass Forage Sci 51:333-342.
Ekanayake, I.J., J.C. O’Toole, D.P. Garrity, T.M. Masajo. 1985. Inheritance of root
characteristics and their relations to drought resistance in rice. Crop Sci.
26(6):927-933.
Falconer, D.S. and T.F.C. MacKay. 1996. Introduction to quantitative genetics. Longman
Grp. Ltd., Essex, England.
Fehr, W. 1987. Principles of Cultivar Development. Vol. 1. Theory and Technique.
Macmillan Publishing Co., NY.
Fribourg, H.A., D.B. Hannaway, and C.P. West. 2009. Tall fescue For the Twenty-first
Century. ASA, CSSA, SSSA. Madison, WI.
Griffing, B. 1956. Concept of general and specific combining ability in relation to diallel
crossing systems. Australian Journal of Biological Science. 9:464-493.
95
Hartl, D.L., E.W. Jones. 2005. Genetics: Analysis of genes and genomes. 6th Edition.
Jones and Bartlett Publishers Inc. Sudbury, MA.
Hayman, B.I. 1957. Interaction, heterosis and diallel crosses. Genetics. 42(3): 336-355.
Huck, M., R.N. Carrow, and R.R. Duncan. 2000. Effluent water: Nightmare or dream
come true. USGA Green Selection Record. March/April. Pgs. 15-29.
Huang, Y., L. Zhang, J. Zhang, D. Yuan, C. Xu, X. Li, D. Zhou, S. Wang, Q. Zhang.
2006. Heterosis and polymorphisms of gene expression in an elite rice hybrid as
revealed by a microarray analysis of 9198 unique ESTs. Plant Mol. Biol. 62(45):579-591.
Johnson, R.A. and G.K. Bhattacharyya. 2007. Statistics Principle and Methods Fifth
Edition. John Wiley & Sons Inc. Hoboken, NJ.
Kirda, C., R. Kanber. 1999. Water, no longer a plentiful resource, should be used
sparingly in irrigation agriculture. In. C. Kirda, P. Moutonnet, C. Hera, and D.R.
Nielsen (eds.) Crop Yield Responses to Deficit Irrigation. Kluwer, Dordrcht.
Kitchens, L.A. 1998. Exploring statistics: A modern introduction to data analysis and
inference. 2nd ed. Duxbury Press, Pacific Grove, CA.
Lehman, V.G. and M.C. Engelke. 1991. Heritability estimates of creeping bentgrass root
systems grown in flexible tubes. Crop Sci. 31(6):1680-1684.
Lynch, M. and B. Wash. 1998. Genetics and Analysis of Quantitative Traits. Sinauer and
Associates Inc. Sunderland, MA.
Milesi, C., S.W. Running, C.D. Elvidge, B.T. Tuttle, R.R. Nemani. 2005. Mapping and
modeling the biogeochemical cycling of turf grasses in the United States.
Environmental Management. 36(3):426-438.
Meyer, W.A. and E. Watkins. 2003. Tall Fescue (Festuca arundinacea). p. 107-127. In
M.D. Casler, and R.R. Duncan (eds.) Turfgrass Biology, Genetics, and Breeding.
John Wiley & Sons Inc. Hoboken, NJ.
Nguyen, H. T. and D. A. Sleper. 1983a. Theory and application of half-sib mating in
forage grass breeding. Theor. Appl. Genet. 64:187-196.
Nguyen, H. T. and D. A. Sleper. 1983b. Genetic variability of seed yield and
reproductive characters in tall fescue. Crop Sci. 23:621-626.
Nyquist, W. 1991. Estimation of heritability and prediction of selection response in plant
populations. Crit. Rev. Plant Sci. 10(3):235-322.
Rebetzke, G.J., R.A. Richards, A.G. Condon, and G.D. Farquhar. 2006. Inheritance of
carbon isotope discrimination in bread wheat (Triticum aestivum L.). Euphytica.
150:97-106.
96
Roach, D.A. and R.D. Wulff. 1987, Maternal effects in plants. Annu. Rev. Ecol. Syst.
18:209-235.
Sleper, D.A. and J.M. Poehlman. 2006. Breeding Field Crops Fifth Edition. Blackwell
Publishing, Ames IA.
Tuinstra, M.R., E.M. Grote, P.B. Goldsbrough, and G. Ejeta. 1997. Genetic analysis of
post-flowering drought tolerance and components of grain development in
Sorghum bicolor (L.) Moench. Mol. Breeding. 3:439-448.
Vogel, K.P. and J.F. Pederson. 1993. Breeding systems for cross-pollenated perennial
grasses. Plant Breed. Rev. 11:251-274
West, C.P. 1994. Physiology and drought tolerance of endophyte infected grasses. Boca
Raton, FL: CRC Press.
Wright, S. 1968. Evolution and the genetics of populations, Vol.1. Genetic and biometric
foundations. Univ. of Chicago Press, Chicago.
Xiong, L.Z., G.P.Yang, C.G. Xu, Q. Zhang, M.A. Maroof. 1998. Relationships of
differential gene expression in leaves with heterosis and heterozygosity in a rice
diallel cross. Mol. Breeding 4:129-136.
Yu, S.B., J.X. Li, C.G. Xu, Y.F. Tan, Y.J. Gao, X.H. Li, Q. Zhang, M.A. Maroof. 1997.
Importance of epistasis as the genetic basis of heterosis in an elite rice hybrid.
Proc. Natl. Acad. Sci. USA. 94:9226–9231.
97
Table 4.1. Description of diallel crosses between summer stress tolerant and summer
stress sensitive tall fescue genotypes including heterosis calculations.
Cross
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Female x
malea
2 x 5 ( S x T)
2 x 6 (S x T)
2 x 10 (S x T)
2 x 15 (S x S)
2 x 21 (S x S)
5 x 2 (T x S)
5 x 6 (T x T)
5 x 10 (T x T)
5 x 15 (T x S)
5 x 21 (T x S)
6 x 2 (T x S)
6 x 5 (T x T)
6 x 10 (T x T)
6 x 15 (T x S)
6 x 21 (T x S)
10 X 2 (T x S)
10 X 5 (T x T)
10 x 6 (T x T)
10 x 15 (T x S)
10 x 21 (T x S)
15 x 2 (S x S)
15 x 5 (S x T)
15 x 6 (S x T)
15 x 10 (S x T)
15 x 21 (S x S)
21 x 2 (S x S)
21 x 5 (S x T)
21 x 6 (S x T)
21 x 10 (S x T)
21 x 15 (S x S)
LSD0.05
a
Number
of
progeny
96
95
96
96
96
96
96
96
96
96
95
95
96
96
96
90
96
96
91
76
91
95
96
63
96
96
96
92
63
96
Mid-parent
mean
quality
5.8
3.6
4.5
4.7
3.0
5.8
5.2
6.1
6.3
4.7
3.6
5.2
3.9
4.1
2.4
4.5
6.1
3.9
5.0
3.3
4.7
6.3
4.1
5.0
3.6
3.0
4.7
2.4
3.3
3.6
SD
1.8
1.1
1.4
1.2
1.4
1.8
2.4
1.8
1.4
2.9
1.1
2.4
1.6
1.5
0.8
1.4
1.8
1.5
1.4
1.9
1.2
1.4
1.5
1.4
1.9
1.4
2.9
0.8
1.9
1.9
Pseudo
F2 mean
quality
5.6
4.4
3.8
4.6
3.4
5.5
4.9
5.5
5.9
5.6
4.0
5.5
4.6
5.0
3.0
4.2
5.7
4.2
3.8
4.1
4.6
5.6
5.2
3.9
4.6
2.9
5.5
3.0
3.2
4.0
SD
1.3
1.4
1.4
1.5
1.1
1.2
1.3
1.3
1.4
1.7
1.3
1.2
1.5
1.3
1.2
1.9
1.6
1.4
1.8
1.5
1.4
2.0
1.4
2.2
1.5
1.6
1.3
0.9
1.5
2.0
Heterosis
t-testb
-0.59
3.21
-2.42
-0.56
1.36
-0.77
-0.68
-1.92
-1.44
1.71
1.59
0.72
2.11
3.08
3.00
-0.99
-1.21
0.93
-4.11
2.09
-0.61
-2.33
3.63
-3.06
2.86
-0.53
1.65
2.95
-0.48
1.01
df
42
69
56
69
45
40
37
42
51
38
67
37
50
48
74
76
48
48
68
48
67
76
50
87
44
61
36
58
53
55
P-valuec
ns
**
*
ns
ns
ns
ns
ns
ns
ns
ns
ns
*
**
**
ns
ns
ns
**
*
ns
*
**
**
**
ns
ns
**
ns
ns
0.43
S = summer stress sensitive, T = summer stress tolerant, selections made during summer of 2010 from
space-plant nurseries at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey.
b
Heterosis effects were determined by testing for differences between mid-parent and pseudo F2 progeny
means.
c
* and ** denote significant differences at P < 0.05 and P < 0.01, respectively, and ns denoting no
significant difference
98
Table 4.2. Description of polycross block using three summer stress tolerant and three
summer stress sensitive tall fescue genotypes.
Maternal
parent
2
5
6
10
15
21
a
Number
of
progeny
96
96
96
95
96
96
Maternal
mean
quality
2.8
6.8
2.3
3.9
4.0
1.5
LSD0.05
0.79
SD
1.3
0.9
0.7
1.2
1.4
0.5
Paternal
mean
qualitya
3.5
3.5
3.5
3.5
3.5
3.5
SD
2.0
2.0
2.0
2.0
2.0
2.0
Mid-parent
mean quality
3.2
4.8
3.0
3.7
3.7
2.7
Pseudo
F2 mean
quality
4.9
5.6
4.8
4.4
6.2
4.2
0.38
Pollen source was considered one homogeneous entity for all crosses. Paternal means and SDs are
averages of all clones involved in the polycross block.
SD
1.5
1.3
1.5
1.7
1.5
1.6
99
Table 4.3. Calculations of maternal effects and minimum gene number estimation in the
full diallel cross.
Cross
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
a
Female x
malea
2 x 5 ( S x T)
2 x 6 (S x T)
2 x 10 (S x T)
2 x 15 (S x S)
2 x 21 (S x S)
5 x 2 (T x S)
5 x 6 (T x T)
5 x 10 (T x T)
5 x 15 (T x S)
5 x 21 (T x S)
6 x 2 (T x S)
6 x 5 (T x T)
6 x 10 (T x T)
6 x 15 (T x S)
6 x 21 (T x S)
10 X 2 (T x S)
10 X 5 (T x T)
10 x 6 (T x T)
10 x 15 (T x S)
10 x 21 (T x S)
15 x 2 (S x S)
15 x 5 (S x T)
15 x 6 (S x T)
15 x 10 (S x T)
15 x 21 (S x S)
21 x 2 (S x S)
21 x 5 (S x T)
21 x 6 (S x T)
21 x 10 (S x T)
21 x 15 (S x S)
Progeny Reciprocal
mean
mean
quality
quality
5.6
5.5
4.4
4.0
3.8
4.2
4.5
4.6
3.4
2.9
5.5
5.6
4.9
5.5
5.5
5.7
5.9
5.6
5.6
4.0
4.0
4.4
5.5
4.9
4.6
4.2
5.0
5.2
3.0
3.0
4.2
3.8
5.7
5.5
4.2
4.6
3.8
3.0
4.1
3.2
4.6
4.5
5.6
5.9
5.2
5.0
3.0
3.8
4.6
4.0
2.9
3.4
5.5
5.6
3.0
3.0
3.2
4.1
4.0
4.6
Maternal
t-testb
0.35
1.96
-1.51
0.06
2.63
-0.35
-3.44
-1.10
1.39
0.24
-1.96
3.44
1.84
-0.90
0.35
1.51
1.10
-1.84
-0.45
3.76
-0.06
-1.39
0.90
0.45
2.63
-2.63
-0.24
-0.35
-3.76
-2.63
df
189
188
166
185
167
189
189
181
165
182
188
189
189
189
178
166
181
189
116
130
185
165
189
116
175
167
182
178
130
175
Pvaluec
ns
ns
ns
ns
**
ns
**
ns
ns
ns
ns
**
ns
ns
ns
ns
ns
ns
ns
**
ns
ns
ns
ns
**
**
ns
ns
**
**
Minimum
number
of genes
2.0
0.2
0.0
0.1
3.9
3.2
4.1
1.4
0.7
2.2
0.2
5.3
0.4
0.9
0.4
0.0
0.6
0.5
0.0
0.9
0.1
0.2
0.7
0.0
1.3
0.4
4.9
-0.8
0.8
0.5
S = summer stress sensitive, T = summer stress tolerant, selections made during summer of 2010 from
space-plant nurseries at the Rutgers Agricultural Experiment Station in Adelphia, New Jersey.
b
Maternal effects were determined by testing for significance in differences between progeny of reciprocal
crosses.
c
** Denotes significance at P < 0.01 level.
100
Figure 4.1. Progeny quality distribution for full diallel cross (a) and polycross block (b),
during the summer of 2012 at the Rutgers Agricultural Experiment Station in Adelphia,
New Jersey.
700
(a)
Mean = 4.6
SD = 1.7
Number of Progeny
600
500
400
300
200
100
0
1
2
3
4
5
6
Quality Rating
7
8
9
160
Number of Progeny
140
(b)
Mean = 5.0
SD = 1.7
120
100
80
60
40
20
0
1
2
3
4
5
6
Quality Rating
7
8
9
101
Figure 4.2. Mid-Parent-progeny regression of six tall fescue parents crossed in a full
diallel design (a) and a polycross design (b) evaluated for summer stress tolerance
observed during the summer of 2012 at the Rutgers Agricultural Experiment Station in
Adelphia, New Jersey.
Progeny Mean (Quality Rating)
7
(a)
6
5
4
3
2
y = 0.6643x + 1.579
r = 0.81
1
1
2
3
4
5
Mid-Parent Mean (Quality Rating)
6
7
6
7
Progeny Mean (Quality Rating)
7
(b)
6
5
4
3
y = 0.4747x + 3.3345
r = 0.59
2
1
1
2
3
4
5
Mid-Parent Mean (Quality Rating)
102
CHAPTER 5
Thesis Conclusions
Growth chamber screening of diverse tall fescue genotypes demonstrated the
difficulty of accurately evaluating summer stress tolerance of turfgrasses not grown under
field conditions. The complexity of summer stress tolerance and the large number of
environmental factors involved make it nearly impossible to accurately recreate realworld conditions in an artificially controlled environment. These data suggest that high
temperatures are a significant component of summer stress responsible for the decline of
tall fescue during summer months. Rainout shelter structures are capable of providing
more realistic field conditions and offer a method of evaluating drought and summer
stress characteristics without having to rely on extended periods without rainfall. When
using these structures, special care must be taken to prevent water from entering the
experimental soil from adjacent unsheltered areas. The use of impermeable barriers along
the interface of sheltered and unsheltered soil will prevent flow of water into the test soil.
High broad-sense heritability estimates are supported by the superior performance
in overall quality ratings of summer stress tolerant selections compared to genotypes
selected as summer stress sensitive. Summer stress tolerant genotypes had significantly
higher performance in 2010 and 2011 in the rainout shelter. Additionally, selections (TF5, TF-6, and TF-10) from the summer stress tolerant germplasm out performed selections
(TF-2, TF-15, and TF-21) from the summer stress sensitive germplasm when planted in
with the diallel and polycross populations. In total, there were differences between the
performances of these two groups over three different years in a total of three different
locations.
103
While the overall performance of these two groups under summer stress remained
constant, variation in the performance of particular clones between years and between
locations demonstrates that summer stress tolerance in tall fescue is not controlled solely
by genetic factors. The non-genetic environmental factors involved in the overall summer
stress tolerance of tall fescue include a litany of atmospheric, edaphic, and biotic
conditions.
Narrow-sense heritability estimates of summer stress tolerance in tall fescue show
progress can be made through cycles of recurrent selection. However, it is important that
progeny be evaluated in multiple locations over multiple years to get an accurate
representation of the genetic drought tolerance.
Further evaluation of the diallel and polycross populations presented in this study
should be performed. To this point, the progeny in these two populations have only been
evaluated over one summer. Further evaluation of the clones and progeny in these
populations will provide more accurate heritability estimates. Evaluation during a single
season could show differences in performance that potentially result from the maturity of
plants.
Additional research, focusing on mechanisms of summer stress tolerance in tall
fescue, would shed more light on this complex problem. A better understanding of the
physiological and biochemical traits that are responsible for the drought tolerance
exhibited by genotypes in this experiment could aid breeders in making selections.
Pinpointing these traits would also potentially facilitate the production of molecular
markers, which would allow breeders to employ marker assisted selection. Marker
assisted selection allows breeders to select the desired genotypes without spending the
104
time and money required to grow large populations in multiple locations to be evaluated
phenotypically.