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RESEARCH
Drought Tolerance of Tall Fescue
Populations Selected for High Root/Shoot
Ratios and Summer Survival
Douglas E. Karcher,* Michael D. Richardson, Kenneth Hignight, and Debra Rush
ABSTRACT
Freshwater resources for turfgrass irrigation are
becoming limited. Hence, the development of
drought tolerant turf cultivars will be of great value
to turf managers. The objective of the following
research was to evaluate the field drought tolerance of turf-type tall fescue (Festuca arundinacea
Schreb.) entries that were selected based either
on high root/shoot ratio under greenhouse conditions or under severe drought stress conditions in
the field. Twelve tall fescue entries (two selected
by root/shoot ratio, two selected by screening
field drought tolerance, the four parents, and
four standard controls) were established under
a rain-out shelter, and their green turf coverage
was evaluated during drought stress (irrigation
withheld) and drought recovery (irrigation reapplied) events in 2003 and 2004. In both years,
entries selected for high root/shoot ratio demonstrated significantly improved drought tolerance
compared to their parents, whereas improved
drought tolerance for field-selected entries was
less consistent. Turf green-up following drought
conditions was correlated to the drought tolerance of each entry, in that those cultivars that
were the most drought tolerant were also the first
to green up on rewatering. These results validate
that selecting germplasm based on high root/
shoot ratio in the greenhouse is a viable method
for improving the field drought tolerance of turftype tall fescue.
D.E. Karcher and M.D. Richardson, Dep. of Horticulture, Univ. of
Arkansas, 316 Plant Sciences Bldg., Fayetteville, AR 72701; K. Hignight and D. Rush, Nexgen Seed Research, LLC, 33725 Columbus St.
SE, Albany, OR 97321-0452. Received 16 May 2007. *Corresponding
author ([email protected]).
Abbreviations: DAI, days after irrigation; FS, field-selected; RS, rootselected.
T
he development of turfgrass cultivars with improved tolerance to limited or low-quality water remains one of the most
important research objectives facing the turfgrass industry, especially
as turf irrigation practices become more restrictive across the United
States. Plants endure or survive water deficits with a variety of escape,
avoidance, and tolerance mechanisms, all of which serve to improve
the efficiency of water uptake, water use, or water loss. Drought
escape is a rather narrow classification and usually refers to plants that
exploit rapid phenological development when water is available, followed by dormancy during severe stress (Kramer, 1980). Although
some turfgrasses can utilize drought escape by going into dormancy
during prolonged drought periods, most turfgrass managers desire
maintaining a green surface during drought periods for aesthetics,
playability, and safety. Therefore, drought escape is only considered
a viable alternative for turfgrasses in those areas where irrigation is
not available and survival of the turfgrass following drought is the
primary objective.
Drought tolerance mechanisms are more readily adapted to
maintained turfgrass systems, as these processes allow the turfgrass to maintain turgor and avoid dormancy. Plant tolerance
to drought stress can be subdivided into those plants that tolerate drought while maintaining a low tissue water potential and
Published in Crop Sci. 48:771–777 (2008).
doi: 10.2135/cropsci2007.05.0272
© Crop Science Society of America
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those plants that tolerate drought by maintaining a high
tissue water potential ( Jones et al., 1981). Plants that tolerate drought while experiencing low tissue water potential
accumulate various solutes in a process termed osmotic
adjustment. Osmotic adjustment allows the plant to maintain turgor under severe low soil water potentials by
decreasing cellular osmotic potential. Osmotic adjustment
has been demonstrated in numerous grasses (DaCosta and
Huang, 2006; Qian and Fry, 1997) and usually involves
the accumulation of compatible solutes such as carbohydrates, amino acids, and mineral ions.
A second grouping of drought tolerance mechanisms
includes those plants that tolerate drought by maintaining
high tissue water potential through reduced water loss or
enhanced water uptake. Plant water loss can be reduced
under water deficit stress by leaf rolling or rapid stomatal
closure and these mechanisms have been demonstrated in
many grasses (Frank and Berdahl, 2001; Xu et al., 2006).
However, this mechanism has negative consequences, as
stomatal closure also reduces CO2 fi xation and can lead
to temperature increases in the canopy due to a drop in
transpirational cooling (Throssell et al., 1987).
Enhanced water uptake through increased root size
and depth is one of the most desirable drought tolerance
mechanisms for turfgrass systems, as this allows the turf to
fully utilize available soil water resources and prolong the
need for supplemental irrigation. This can be especially
beneficial in areas where rainfall is sporadic during the
summer season, as the ability of the plant to maintain a
favorable water balance until the next rainfall event could
greatly minimize the need for supplemental irrigation
while producing an acceptable quality turf.
Recently, techniques have been described to screen
turfgrass germplasm for enhanced rooting characteristics
by germinating seedlings in a polyethylene glycol solution
and subsequently selecting plants in a controlled environment having a high root/shoot ratio (Bonos et al., 2004).
Bonos and coworkers were able to achieve up to 81 and
130% gains in root/shoot ratios following two generations of selection of turf-type tall fescue (Festuca arundinacea
Schreb.) and perennial ryegrass (Lolium perenne L.) varieties,
respectively. If these gains translate to improved drought
tolerance in the field, these techniques may expedite the
development of drought tolerant cultivars compared to traditional screening methods. The objective of this research
was to validate field drought tolerance of tall fescue populations and cultivars selected for either enhanced root/shoot
ratios in the greenhouse or selected under extreme drought
conditions in a field environment.
MATERIALS AND METHODS
Experimental Area
All studies were conducted at the Nexgen Seed Research, LLC
research facilities in Albany, OR (44°33a N, 123°04a W), dur772
ing the 2003 and 2004 growing seasons. In fall of 2002, tall
fescue selections (Table 1) were seeded at 29 g m–2 into 1.0
by 1.0 m plots on a native silt-loam soil (Woodburn silt loam,
fi ne-silty, mixed, superactive, mesic Aquultic Argixeroll, pH
5.6–6.5, organic matter 3–5%). Each entry was replicated four
times in a randomized complete block experimental design. The
experimental area was covered with a rain-out structure consisting of a 6-mm-ply clear plastic top and removable fiberglass
sides to minimize air-flow restriction while preventing precipitation from reaching the plots. The area was irrigated with
Netafi m overhead sprinklers (inverted BR-O spinner/antimist;
Netafi m, Fresno, CA) positioned 180 cm above ground level
and attached to the rain-out structure. Irrigation was provided
as needed during establishment to promote germination and
establishment and at a rate of 2.5 cm wk–1 thereafter to provide optimal growing conditions. Following establishment, the
experimental area was mowed 2 times per week at a height of
2.5 cm in 2003. In 2004, the mowing height was decreased to
1.6 cm to further enhance drought stress symptoms across the
experimental area. Fertilizer was applied in March and April of
each season with a 19-3-16 (N-P2O5 -K 2O) product (Woodburn
Royal Green, Woodburn Fertilizer, Inc., Woodburn, OR) at a
rate of 19 g m–2.
Experimental Entries
Twelve tall fescue cultivars or experimental entries were
included in these trials. The cultivars Bonsai, Kentucky-31,
Plantation, and Southeast were included as check varieties since
these have been widely used in the turfgrass industry and cultivars such as Southeast have been promoted as having improved
drought tolerance (Carrow and Duncan, 2003). Other entries
in the trial included the cultivars Axiom, Wyatt, Regiment, and
Tulsa, which had been developed by the Nexgen Seed Research
breeding program. From each of these cultivars, advanced plant
material was developed either through the root-selected (RS)
program described earlier (Bonos et al., 2004) or were selected
by exposing populations of germplasm to extreme heat and
drought stress under field-selected (FS) conditions in Griffin,
GA, over several years and selecting surviving plants for recombination (Carrow and Duncan, 2003).
The experimental entries not only differed in how they
were selected, but also the genetic diversity in the parent material. The Wyatt population represented a narrow genetic base
population, selected from one cultivar, while Axiom had a
much broader genetic base population and was selected from
seven cultivars. It should also be noted that the Tulsa (FS) entry
tested in this trial has been commercialized and released as the
cultivar Greystone.
Drought Stress and Recovery Evaluations
On 17 May 2003 and 24 June 2004, the experimental area was
saturated with 5 cm of irrigation per day for three consecutive
days to eliminate any dry areas and produce uniformly wet conditions across all plots. Immediately thereafter, irrigation was
withheld to encourage drought stress symptoms. The response
of entries to drought stress was evaluated weekly using digital
image analysis techniques (Richardson et al., 2001) to quantify
the percent green turf cover for each plot as drought became
more severe. In both years, when all plots had fallen below 25%
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green turf cover, the experimental areas were saturated with
5.0 cm of irrigation to initiate drought recovery (29 and 30
Aug. 2003 and 2004, respectively). Thereafter, the experimental area was irrigated weekly with 2.5 cm water and recovery
from drought was evaluated weekly using digital image analysis
until plots reached 100% green cover.
Before the onset of drought, plots were visually evaluated
for general turfgrass performance characteristics, including turfgrass quality, genetic color, and turfgrass density. All ratings were
made on a scale of 1 to 9, with 9 being optimal turfgrass quality,
dark green genetic color, or maximum turfgrass density.
where DAI = days after irrigation (ceased or initiated, for drydown or green-up, respectively) and days50 and slope are estimated model parameters. Days50 is estimated to be the DAI
when green turf cover equals 50%. The slope parameter defi nes
how rapidly turf cover changes over time with larger positive or
negative values representing steeper positive or negative slopes
of the sigmoid curve.
A sum of squares reduction F-test was used to determine if
tall fescue entries significantly affected green turf cover during
drought stress and drought recovery (Motulsky and Christopoulos, 2003). The F-test compared the sum of squares from a
global model (all varieties share days50 and slope values) against
the cumulative sum of squares from models where days50 and
slope values were determined separately for each variety. If the
sum of squares were reduced significantly (P < 0.05) using separate parameter values, variety effects were determined to be
significant. Parameter estimates were used to calculate confidence intervals (95%) for the number of DAI (irrigation ceased
or initiated) until each entry reached 25, 50, and 75% green
turf color (Motulsky and Christopoulos, 2003). At each turf
coverage percentage (25, 50, and 75), entries were considered
Statistical Analysis
Scatter plots of the percent green turf cover data versus days
after irrigation withheld during drought stress, and days after
irrigation applied during drought recovery, indicated a strong
nonlinear relationship. Furthermore, the data fit very well to a
sigmoid variable slope model,
[1]
Table 1. Parameters for predicting the dry-down and green-up characteristics of tall fescue entries. Smaller (more negative)
slope values translate to more rapid changes in green cover over time. Days50 is the predicted number of days (from irrigation
withheld or applied) until the turf reaches 50% green cover.
Variety †
Slope
SE
2003
Days50
SE
R2
Slope
SE
2004
Days50
SE
R2
Dry-down
Axiom
–0.068
0.0035
48.7
0.37
0.98
–0.064
0.0059
43.1
0.67
0.97
Axiom (RS)
–0.034
0.0042
59.2
1.51
0.76
–0.042
0.0037
54.3
0.96
0.92
Bonsai
–0.047
0.0065
47.7
1.36
0.79
–0.049
0.0065
47.6
1.29
0.90
Kentucky-31
–0.044
0.0055
52.4
1.32
0.81
–0.038
0.0047
51.8
1.48
0.87
Plantation
–0.055
0.0041
46.0
0.64
0.94
–0.049
0.0054
47.7
1.09
0.93
Regiment
–0.056
0.0039
48.7
0.59
0.95
–0.064
0.0064
41.4
0.73
0.96
Regiment (FS)
–0.049
0.0044
51.6
0.87
0.90
–0.052
0.0036
46.5
0.63
0.97
Southeast
–0.052
0.0046
47.3
0.80
0.92
–0.048
0.0033
44.8
0.68
0.97
Tulsa
–0.042
0.0033
53.7
0.83
0.91
–0.043
0.0041
46.4
1.01
0.94
Tulsa (FS)
–0.048
0.0048
50.2
0.96
0.89
–0.041
0.0028
52.2
0.77
0.96
Wyatt
–0.055
0.0035
49.4
0.55
0.96
–0.056
0.0043
40.4
0.63
0.97
Wyatt (RS)
–0.048
0.0023
53.5
0.48
0.97
–0.043
0.0031
46.8
0.78
0.96
Mean
–0.050
0.90
–0.049
50.7
46.9
0.94
Green-up
Axiom
0.110
0.0072
9.3
0.28
0.97
0.083
0.0108
11.7
0.74
0.94
Axiom (RS)
0.081
0.0073
5.7
0.47
0.90
0.098
0.0074
4.7
0.37
0.98
Wyatt
0.080
0.0069
9.7
0.48
0.92
0.060
0.0094
13.1
1.13
0.89
Wyatt (RS)
0.094
0.0057
7.6
0.29
0.96
0.075
0.0083
8.3
0.67
0.95
Regiment
0.082
0.0065
10.4
0.45
0.94
0.092
0.0130
10.2
0.73
0.94
Regiment (FS)
0.087
0.0068
8.7
0.41
0.93
0.096
0.0109
8.1
0.57
0.96
Tulsa
0.081
0.0064
7.7
0.43
0.93
0.093
0.0104
7.5
0.58
0.96
Tulsa (FS)
0.070
0.0058
10.2
0.53
0.92
0.110
0.0091
5.1
0.38
0.98
Bonsai
0.056
0.0065
10.5
0.90
0.82
0.102
0.0096
7.1
0.45
0.97
Kentucky-31
0.080
0.0073
7.8
0.50
0.90
0.088
0.0117
5.7
0.71
0.93
Plantation
0.074
0.0055
11.1
0.46
0.94
0.101
0.0129
8.1
0.60
0.95
Southeast
0.070
0.0064
9.8
0.57
0.90
0.085
0.0066
8.4
0.43
0.98
Mean
0.080
0.92
0.090
†
9.1
8.2
0.95
FS, field-selected; RS, root-selected.
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773
RESULTS AND DISCUSSION
significantly different if their confidence intervals did not overlap. Nonlinear regression analysis of the turf cover data was
performed using GraphPad Prism version 4.0 for Windows,
(GraphPad Software, San Diego, CA). Visual rating data was
analyzed using a one-way ANOVA to determine if turfgrass
selection effects were significant (P < 0.05) and means were
separated using Fisher’s protected least significance difference
test (B = 0.05).
Tall fescue entry significantly affected green turf coverage
during both drought stress and drought recovery in both
years of the study (Table 2). The sigmoid models used to
predict turf coverage (Fig. 1) provided a good fit of the
green turf cover data, resulting in average R2 values of 0.90
and 0.94 during drought stress in 2003 and 2004, respectively, and 0.92 and 0.95 during drought recovery
Table 2. Hypothesis test summaries for tall fescue entry effects on green in 2003 and 2004, respectively (Table 1).
Reproduced from Crop Science. Published by Crop Science Society of America. All copyrights reserved.
turf coverage during dry-down and green-up events in 2003 and 2004.
Sum of squares
reduction test
Null hypothesis
Alternative hypothesis
Dry-down
2003
Drought Stress
Green-up
2004
2003
2004
Shared regression parameters (slope and days50)† for all varieties
Different regression parameters for each variety
Numerator df
22
22
22
22
Denominator df
588
346
660
192
F value
8.71
11.77
6.66
8.88
P value
<0.001
<0.001
<0.001
<0.001
†
Slope and days50 values determine percent green turf cover according to Eq. [1].
Figure 1. Predicted dry-down curves for tall fescue entries in 2003 and 2004.
774
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In both years of this trial, tall fescue entries
began to show initial symptoms of drought
stress, as measured by loss of green color, at
approximately 20 d after withholding irrigation.
Tall fescue entries generally lost green cover
more quickly in 2004 than in 2003, declining
to 50% green cover at 47 and 51 DAI withheld
(on average), respectively (Table 1, Fig. 1). This
was likely the result of lowering the mowing
height from 2.5 cm in 2004 to 1.6 cm in 2003
(temperatures were similar between years).
Axiom (RS) demonstrated the best drought
tolerance throughout the trial, reaching 75%
green cover at 45 and 43 DAI withheld in 2003
and 2004, respectively. Axiom (RS) was also
the last entry to reach both 50% and 25% green
cover in both years of the trial (Fig. 2). Tulsa
(FS) and Kentucky-31 in 2004 were the only
entries that exhibited a similar level of drought
tolerance in the trial.
Entries that exhibited the least drought
tolerance, as measured by days to reach 25%
green cover, included the cultivars Plantation, Axiom, Southeast, Regiment, Bonsai,
and Wyatt in 2003 and Wyatt, Regiment, and
Axiom in 2004 (Fig. 2). In 2003, the most
drought tolerant entry, Axiom (RS), reached
50% green cover 13.2 d later than the least
drought tolerant cultivar, Plantation (Table
1). In 2004, Axiom (RS) was again the most
drought tolerant cultivar and reached 50%
green cover 13.0 d later than Wyatt, the entry
with the least drought tolerance (Table 1).
These results clearly demonstrate that tall
fescue variety can have a significant impact on
turf responses to long-term drought stress. In
some instances, there was as much as a 10-d
difference between entries in respect to the
onset of drought stress symptoms (Fig. 1). This
could have a significant impact on supplemental irrigation requirements over an entire
growing season, especially in humid regions,
where periodic rain can significantly reduce or
CROP SCIENCE, VOL. 48, MARCH– APRIL 2008
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even eliminate the need for irrigation. In those instances, the delay
of drought stress symptoms would
delay the need for supplemental
irrigation and provide additional
opportunity for rainfall to occur.
It is also evident from these
data and previous studies (Carrow
and Duncan, 2003) that breeding
efforts can improve the drought
tolerance of tall fescue cultivars.
Breeding populations that were
selected either in the RS trials
(Bonos et al., 2004) or in field trials
(Carrow and Duncan, 2003) generally had delayed drought stress
symptoms when compared to the
parent populations (Table 1, Fig. 2
and 3). In both the 2003 and 2004
trials, the Axiom (RS) and Wyatt
(RS) entries had significantly
delayed drought stress symptoms
compared to the parent cultivars,
Axiom and Wyatt (Table 1, Fig.
2 and 3). For both populations, a
delay in drought stress symptoms
(to decline to 25% green cover) of
7 to 16 d was observed with the RS
populations compared to the parent cultivars (Fig. 2). These results
suggest that selecting plants with
enhanced rooting capabilities during the establishment phase (Bonos
et al., 2004) can translate to greater
rooting and better drought tolerance in the field. Although root data
were not collected in this trial, it
would seem apparent that the delay
in drought stress symptoms would Figure 2. The 95% confidence intervals for the number of days after water was withheld until tall
represent continued water uptake fescue entries reached 75, 50, and 25% green cover in 2003 and 2004. Within each year and
green cover percentage, entries with overlapping bars were not significantly different.
by drought tolerant entries.
The genetic diversity of the
tage over the parent, Wyatt (Table 1). These results supbase populations used for the original screening also was
port the earlier findings of Bonos et al. (2004), that faster
related to drought tolerance of the entries tested in this
gains in drought tolerance can be achieved by using broad
trial. As noted by Bonos et al. (2004), larger gains in root
genetic populations for screening.
mass were observed when tall fescue was selected from
The field screening of germplasm for enhanced
a broad population (81% increase) compared to a nardrought tolerance did not produce a consistent advantage
row population (41% increase). In the present trial, simiin drought tolerance compared to the RS techniques. In
lar differences were observed with respect to the onset of
both years, Regiment (FS) had delayed drought stress
drought stress symptoms. Axiom (RS), which was origisymptoms compared to Regiment, as evident by signifinally selected from a broad genetic population, averaged
cant differences in days to both 50 and 25% green cover
an 11-d delay in drought stress symptoms compared to the
(Fig. 2). However, the Tulsa (FS) populations were actuparent population, Axiom, while Wyatt (RS), a selection
ally inferior to the original cultivar in the 2003 trial and
from a narrow genetic base, only averaged a 5-d advanCROP SCIENCE, VOL. 48, MARCH– APRIL 2008
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775
physical and chemical properties that could
restrict root growth and significantly influence the plant’s ability to survive extended
drought periods.
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Drought Recovery
Drought recovery, as measured by green-up
of the plots was significantly affected by tall
fescue entry in both years of the trial (Tables
1 and 2). However, it was apparent from the
data that entries that were last to go completely
dormant during the dry-down (Table 1) were
also the first entries to green-up in each year of
the trial (Table 1). This is not surprising, since
those entries that were the fi rst to experience
severe water stress were under that stress for a
much longer period and would naturally be
slower to recover after the stress was removed.
Nonetheless, these results further point out the
importance of delayed drought stress in maintaining turfgrass quality during cyclic water
availability. However, the study does not allow
a direct comparison of recovery from drought
stress since entries were not exposed to drought
stress for similar periods of time.
Figure 3. Digital images of tall fescue entries taken at 53 d after drought stress was
imposed on plots in 2003. Numbers in parentheses represent the percentage of
green tissue in the plot, as determined by digital image analysis.
exhibited earlier symptoms of drought stress (Fig. 2). In
the 2004 trial, the opposite was observed, in that the
Tulsa (FS) entry had delayed drought stress compared to
the Tulsa entry (Fig. 2). Although it is unclear why these
differences existed between the 2 yr of the trial, it is possible that the Tulsa (FS) population needed to be more
mature before enhanced drought tolerance was expressed.
In addition, these differences may also reflect a differential response of some entries to a lower mowing height in
2004 compared to 2003.
An interesting aspect of these results was the apparent lack of drought tolerance in the cultivar Southeast,
which had been previously reported to have reduced leaf
fi ring and enhanced drought tolerance relative to other
tall fescue populations (Carrow and Duncan, 2003). In
the present study, all entries were grown in a deep, fertile soil with moderate pH levels, while Southeast was
selected and previously tested in shallow, infertile soils
with low pH (<4.5) (Carrow and Duncan, 2003). The
advantages in drought tolerance and survival previously
observed with Southeast may be more related to its ability to grow under difficult soil conditions, or under conditions of high humidity, and not just a single increase
in rooting capacity and drought tolerance. Future studies
with these and other cultivars should include other soil
776
Turfgrass Performance
The entries tested in this trial exhibited a wide
range of color, density, and turfgrass quality
scores (Table 3). Two cultivars, Kentucky-31 and Southeast, had poor color, density, and quality compared to all
other cultivars and especially entries such as Plantation and
Tulsa (FS) (Table 3). These results demonstrate that newer
turf-type cultivars of tall fescue can be developed that
produce both high turfgrass performance ratings, while
also exhibiting improved drought tolerance compared to
older, forage-type cultivars such as Kentucky-31. Collectively, these results suggest that further improvements in
drought tolerance of tall fescue should be attainable without sacrificing desirable performance characteristics such
as color and density.
CONCLUSIONS
Improvement in drought tolerance for entries selected for
high root/shoot ratio was consistently as good, or better, than for entries selected by traditional field screening.
Moreover, the root/shoot selection from Axiom was the
only top-performing entry with regard to drought tolerance throughout both study years. Therefore, selecting
plant material based on greenhouse rooting characteristics
appears to be an efficient means to develop turf-type tall
fescue varieties with improved drought tolerance. In addition, the use of a rain-controlled facility coupled with the
precise measurements of green cover attainable with digital
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CROP SCIENCE, VOL. 48, MARCH– APRIL 2008
Table 3. Turfgrass performance characteristics, evaluated before the onset of drought stress.
Entry †
2003
Color
Density
2004
Quality
Color
Density
Average
Quality
Color
Density
Quality
‡
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———————————————————————————— 1–9 scale ————————————————————————————
Tulsa (FS)
6.2
6.0
5.8
6.4
6.4
6.5
6.3
6.2
6.2
Plantation
6.5
5.8
5.6
7.0
6.0
6.3
6.8
5.9
6.0
Axiom (RS)
6.4
5.8
6.0
5.2
5.6
5.8
5.8
5.7
5.9
Tulsa
5.6
6.3
5.7
6.2
6.3
6.0
5.9
6.3
5.9
Axiom
6.0
5.5
6.1
5.6
5.1
5.5
5.8
5.3
5.8
Regiment
5.0
5.8
5.7
5.7
5.9
5.8
5.4
5.8
5.7
Bonsai
4.8
6.9
5.5
5.2
5.8
5.8
5.0
6.3
5.6
Wyatt
5.1
6.2
5.7
7.0
5.8
5.6
6.0
6.0
5.6
Wyatt (RS)
5.7
5.6
5.3
6.5
5.7
5.7
6.1
5.7
5.5
Regiment (FS)
5.0
5.9
5.2
6.0
5.2
5.4
5.5
5.5
5.2
Southeast
4.1
4.1
4.7
3.6
4.0
4.1
3.8
4.1
4.4
Kentucky-31
4.6
3.3
4.4
2.8
3.4
3.7
3.7
3.4
4.0
LSD§
0.8
0.3
0.5
0.8
0.6
0.5
0.5
0.4
0.3
†
FS, field-selected; RS, root-selected.
‡
9 = optimum color, density, or quality.
§
LSD, least significant difference between means within a column at (B = 0.05).
image analysis proved to be an effective means of evaluating
the drought tolerance of a wide range of grasses with relative ease. Future studies should apply similar techniques to
other cool- and warm-season turfgrasses to identify germplasm with superior drought tolerance characteristics.
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