Evaluation of Four Treatments to Break Seed Dormancy
of Sunflower Inbreds
A Research Study Presented for the
Master of Science in
Agriculture and Natural Resources Degree
University of Tennessee at Martin
Submitted by: Rogelio Marchetti
December 2012
ii ABSTRACT
Seed dormancy can be a major problem for seed companies. In sunflower (Helianthus
Annuus, L.) breeding programs, dormancy limits the number of crop cycles per year; it also leads
to asynchronous blossom times, restricting the opportunity to make crosses between plants. This
study evaluated simple techniques to break dormancy in sunflower. A preliminary laboratory
study confirmed that only 32% of non-treated plants emerged, whereas exposure of seed to a
cold treatment improved the germination to 92%. The subsequent field experiment tested four
treatments intended to break possible dormancy effects. Six sunflower inbred lines were grown
and harvested 30 days after flowering to assure enough time for embryo development while
promoting dormancy. The first two treatments were aimed at removing physical dormancy by
chipping a minuscule section of the pericarp or by exposing the seed to temperature oscillation to
degrade impermeable layers. The other two treatments worked at the hormone level of dormancy
by placing seeds in a saturated atmosphere of ethylene gas or by submerging the seed in ethrel
(liquid ethylene). The four treatments were compared to a control, in which seeds were kept in
the cold at night and at room temperature during day. The experiment was arranged in a split plot
randomized complete block design (RCBD) and evaluated with analysis of variance. The highest
mean emergence was obtained in the control (54%) and temperature oscillation (52%)
treatments. Mean emergence for the seed chipping treatment was 32%, which was significantly
(P<0.05) lower than all other treatments. However, there was a significant (P=0.0062) interaction
between treatments and lines. Although some of the treatments increased germination in some
lines, they also depressed germination in other inbreds. No treatment improved germination
consistently over the control while most of them added complexity to seed handling.
iii Table of Contents
Page
Chapter I. – Introduction .............................................................................................................1
Economic importance ...................................................................................................................1
Objective .....................................................................................................................................4
Chapter II. – Literature Review ...................................................................................................5
Seed germination ..........................................................................................................................5
Sunflower .....................................................................................................................................7
Dormancy in sunflower seeds ......................................................................................................9
Hormones ...................................................................................................................................10
Breaking seed dormancy ............................................................................................................11
Chapter III. – Materials and Methods .......................................................................................13
Site description ...........................................................................................................................13
Material selection .......................................................................................................................13
Experimental treatments .............................................................................................................15
Experimental design ...................................................................................................................16
Data collection............................................................................................................................17
Statistical analysis ......................................................................................................................17
Chapter IV. – Results and Discussion ........................................................................................18
Chapter V. – Conclusions ............................................................................................................20
Literature Cited ...........................................................................................................................21
iv List of Tables
Page
Table 1. Sunflower production by country. .................................................................................... 2
Table 2. Germination of six sunflower inbreds using warm and cold germination tests.............. 14
Table 3 List of treatments tested for breaking dormancy in sunflower inbreds. .......................... 15
Table 4. ANOVA table for percent emerged plants of dormant Sunflower inbreds. ................... 18
Table 5. Germination percentage for each seed treatment ............................................................ 18
Table 6. Germination percentage by seed treatment and sunflower line ...................................... 19
v List of Figures
Page
Figure 1. Sunflower production areas. ............................................................................................ 2
Figure 2. The three phases and physiological processes of germination ........................................ 7
Figure 3. Seed dormancy and the control of germination ............................................................. 11
Figure 4. Layout of research plots in the field using a split plot randomized complete block
design. ............................................................................................................................ 16
vi CHAPTER I – Introduction
Sunflower (Helianthus annuus L.) is an annual plant native to North America that
belongs to the Compositae (Asteraceae) family. This family is distinct in that the inflorescence is
formed by hundreds of flowers acting as one. The slim and long flowers that encircle the
sunflower inflorescence, called “ray flowers”, are sterile and their main purpose is to attract
insects. The disk florets, in the center of the inflorescence contain fertile tubular flowers that will
produce achenes, the main interest of this crop. Wild sunflowers are an open pollinated and self
incompatible species; thus wind and insects play a vital role in the reproductive process.
Breeding techniques improved self compatibility in commercial hybrids; however, the presence
of insects is required for seed production (USDA, 2000).
Economic Importance
Due to the high oil content, sunflower seed is primarily crushed and consumed as one of
the most important edible oils. High oleic hybrids that produce seed containing more than 80%
oleic acid are becoming more desirable because they provide a healthier option for human
consumption, placing sunflower into the economically generous specialty sector (Putnam et al.,
1990).
Besides oil, sunflower has many other uses; confectionary hybrids are utilized in the food
industry, whereas bird seeds and sunflower pellets are part of the feed industry. Sunflower is also
finding new markets and can be used to produce biodiesel (Putnam et al., 1990).
1 Wide adaptation of sunflower allows it to be planted worldwide (USDA, 2000). Due to
low costs of production, good market price and robust performance, it is usually grown in dry
areas with poor soil conditions, limiting the true potential yield of this crop (Figure 1).
Russia is the top producer of sunflower seed, followed closely by Europe and Ukraine
(Table 1). Sunflower production is distributed among many countries compared to other crops,
where two to three countries grow a big portion of the global volume.
Figure 1. Sunflower production areas (www.wikipedia.com).
Table 1. Sunflower production by country – FAO, 2010 (www.fao.com).
Rank
1
2
3
4
Country
Russia
EU
Ukraine
Argentina
World Total
2 106 M Tons
7.4
6.9
6.3
3.6
33.4
Throughout history, natural selection, along with selection by humans, shaped sunflower
to its present-day phenotype. Current hybrids are quite different from wild sunflowers; they are
single headed, short plants with a short pollination period (USDA, 2000). The major impacts on
crop improvement and yield of sunflower have been made through plant breeding techniques.
Agronomic traits including disease, insect and herbicide resistance and soil and longitude
adaptation have been added to commercial hybrids through plant breeding.
Whereas plant breeders of other crops, such as soybeans and maize, utilize the latest
techniques in biotechnology making faster improvements with transgenes, sunflower breeders
face a different reality. Potential drift of transgenic events to wild sunflowers and consumer
reluctance to accept genetically modified foods thwart the possibility of utilizing biotechnology
in sunflower (N.S.A., 2000). Today, sunflower breeders rely only on conventional techniques; it
may take up to 15 years to develop and release a new hybrid. To reduce this time frame, most
seed companies implement “winter nurseries,” which are off-season locations that enable
breeders to complete up to three crop cycles in one year, reducing the total number of years to
develop a new inbred to four. Although the benefits of using winter nurseries are worthwhile,
some challenges arise. At harvest the seed is not fully developed and when trying to minimize
days between harvest and planting, germination problems may affect the subsequent planting. A
study on wild sunflower shows that seed maturation influences germination, and seeds are most
mature at 21 days after flowering (Seiler, 1993). Late and uneven emergence are signs of
dormancy issues. If plants do not develop at the same pace, pollination synchrony becomes a
problem, reducing the possibility of making crosses.
3 Objective
The main purpose of this study was to evaluate economical and simple techniques to
remove or reduce dormancy effects in seeds of sunflower inbreds. Reducing dormancy will
enable breeders to:

Replant nurseries faster to achieve three crop cycles per year.

Obtain homogeneous emergence.

Promote uniform parent - progeny blossom times to enable crossing among inbreds.
4 CHAPTER II – Literature Review
Seed Germination
Crop establishment is the first step and one of the most important stages in the vegetative
cycle of crop plants. Uneven emergence and low stand density will compromise the subsequent
stages of growth, limiting potential yield and economic outcome. Growers work to provide the
right conditions for planting: preparing a proper seedbed (moisture and texture), selecting an
appropriate variety, planting at the right time and depth, using a seed treatment, etc.
Unfortunately there are aspects over which farmers have no control and they must rely on the
seeds to emerge rapidly and evenly from the soil.
Nonogaki et al. (2010) notes that germination starts with water imbibition followed by
physiological changes in the seed and is complete with the appearance of the radicle through the
seed structures. The authors explain germination through three phases:
Phase I:
Due to a negative water potential the seed rapidly absorbs water until the cells are
completely hydrated. This crucial step re-activates the seed from a hibernation state with
physiological and chemical changes. Probably the most important change is the resumption of
energy metabolism. Mitochondria and enzymes increase the rate of respiration providing energy
to sustain this rapid growth. Structures and organelles that were damaged during the drying and
re-hydration processes are repaired and replaced. Residual mRNAs, which are formed during
seed development, survive desiccation and contribute to the fast restoration process after
imbibition. Later new mRNA’s are created to continue with protein synthesis (Nonogaki et al.,
2010).
5 Phase II:
During this stage, water uptake decreases, forming a plateau (Fig. 2). Cells are now turgid
and hormones take over the process. The most influential hormones in seed germination are
abscisic acid (ABA) and gibberellic acid (GA). ABA is utilized as a messenger within a plant to
suspend growth. ABA is involved in leaf abscission and also in preventing germination when
environmental conditions are not adequate. On the other side, GA has positive effects on
germination; it is a precursor of alpha-amylase, an enzyme that mobilizes seed reserves. The
interaction or balance between these two antagonistic compounds is what triggers germination.
The presence of ABA deactivates GA and reduces GA biosynthesis while the opposite effect is
found when GA concentration is higher than ABA. Environmental factors such as temperature,
light,
nutrition,
and
smoke
regulate
ABA:GA
ratio,
controlling
germination.
During phase II, fully hydrated cells impose pressure on the soaked and surrounding weakened
structures of the seed, allowing the radicle to emerge. At this point, the second phase, as well as
germination, is completed (Nonogaki et al., 2010).
Phase III:
The last stage, also called postgermination, is the visible growth of the radicle. This
process is characterized by an increase in water uptake, cell division and reserve mobilization.
The seedling also grows, based on mitotic division and cell enlargement (Nonogaki et al., 2010).
6 Figure 2. The three phases and physiological processes of germination (Nonogaki et al. 2010)
Sunflower
The center of origin of sunflower is located in the central plains of North America (Harter
et al., 2004). This plant produces fruits called achenes, which are non-dehiscent fruits surrounded
by the pericarp (external hull), with the actual seed inside. Throughout history, wild sunflowers
have survived extreme weather conditions, diseases, and pests. Dormancy is a survival
technique, similar to hibernation in animals, which prevents seed from germinating until
favorable conditions are present.
Mercer et al. (2006) compared wild sunflower accessions from different parts of the
United States with pure sunflower inbreds. The researchers made various crosses between them
and studied the degree of dormancy of the progeny. Parents and hybrids were planted in the field
and results showed that wild-crop hybrids prevail over wild-wild crosses, giving higher
7 percentage of germination (65% for wild-crop versus 34% for wild-wild) and less dormancy
(58% for wild-crop and 27% for wild-wild). Wild-wild hybrids struggled to survive and
remained dormant for longer periods. This evidence indicates that the parents of sunflower
hybrids have a strong influence in determining dormancy.
Dormancy can be biologically described as: “The absence of germination of an intact,
viable seed under germination favoring conditions with a specific time lapse” (Hilhorst, 1995).
There are different mechanisms and processes involved in seed dormancy. Baskin and Baskin
(2004) divided seed dormancy into five types:
1) Physiological dormancy (PD)
Physiological dormancy is the most common dormancy present in angiosperm and
temperate species, including Helianthus annuus (sunflower), Lycopersicon esculentum (tomato),
and Lactuca sativa (lettuce). Internal changes at the hormone level are needed for the seed to
germinate. This group varies from deep dormancy (3-4 months) to nondeep (less than one
month) (Baskin and Baskin, 2004).
2) Morphological dormancy (MD)
This group presents small but differentiated embryos that have no physiological
dormancy. They require more time for the embryo to mature in order to germinate. Example:
Apium graveolens (Baskin and Baskin, 2004).
3) Morphophysiological dormancy (MPD)
Seeds with morphophysiological dormancy are characterized by small and differentiated
embryos but also have physiological dormancy. Thus they need more time to grow plus a
8 treatment to overcome dormancy such as stratification or GA treatment (Baskin and Baskin,
2004).
4) Physical dormancy (PY)
Physical dormancy is caused mainly by impermeable seed coats that prevent water
uptake. Thick and lignified cell walls are responsible for this physical barrier; water repellent
compounds (waxes, cutin and suberin) that cover the seed can also limit water uptake. Until the
external layers become permeable to water by temperature oscillation, by seed going through the
digestive system of animals, or by freezing and thawing cycles, the germination process will not
start (Baskin and Baskin, 2004).
5) Combination dormancy
Seeds in this group show a combination of physical dormancy accompanied by
physiological dormancy. To overcome dormancy, seeds need to break PY first, allowing water
permeability, and, once imbibed, the embryo will release PD after stratification (Baskin and
Baskin, 2004).
Dormancy in sunflower seeds
A study by Brunick (2007) at the University of Oregon showed that sunflower genotypes
presenting pericarp and coat dormancy are the most difficult to include in breeding programs due
to the complexity of the genes involved, whereas embryo dormancy tends to be more malleable.
In this study, the researchers demonstrated that the number of layers of seed coat plays a crucial
role in imposing extensive dormancy. Wild sunflower seeds tend to be sturdier, having more
layers, while commercial sunflower seeds allow water and oxygen to flow through the
9 teguments, facilitating germination. Another important finding in this research is the response to
daylight. Although sunflower is not greatly affected by this environmental signal, Brunick (2007)
found that germination was greater in light compared to the dark. He recommends alternating 12
hours of light with 12 hours of dark to maximize germination.
Hormones
Hormones play a decisive role in seed dormancy. Finch-Savage and Leubner-Metzger
(2006) describe the relationship between the ABA and GA: germination is not an absolute
process that responds to the presence or absence of one or the other hormone. It is a proportion
or ratio balance where the predominance of one over the other creates a gradual change.
Figure 3 describes the effect of the environment on the ABA:GA ratio and ultimately on
germination (Finch-Savage and Leubner-Metzger, 2006). In the perception phase, external
factors such as light, temperature and water create signals to genes responsible for the synthesis
and degradation of ABA and GA. During the integration phase, the balance of ABA:GA
orchestrates the subsequent steps transferring into the response stage. When environmental
conditions promote ABA prevalence, this triggers more ABA synthesis and GA degradation,
causing the seed to stay dormant. Under favorable conditions, GA synthesis prevails, causing
ABA catabolism and germination initiation.
10 Figure 3. Seed dormancy and the control of germination (Finch-Savage
and Leubner-Metzger 2006)
Breaking seed dormancy
Just as there are different types of dormancies, there are different methods to overcome it.
For example, if a seed presents physiological dormancy, the application of exogenous hormones
or exposure to varying temperatures will remove it.
Water imbibition has many positive effects on removing dormancy. Maiti et al. (2006),
successfully utilized priming, where seeds are submerged in water for 12-24 hours, to effectively
break dormancy in sunflower seeds. Priming works first by activating the germination process.
Secondly, it works by washing away ABA and other compounds that have negative effects on
11 germination. Lastly, imbibition weakens teguments and hard structures, thereby removing
physical dormancy.
Pallavi et al. (2010) utilized temperature treatments to break dormancy of sunflower
seeds. Temperature treatments of 60oC for 15 minutes significantly increased germination over
control by desiccating waxes, weakening the impermeable layer, and allowing water to be
absorbed.
Growth regulators have a positive effect on germination. Application of exogenous
compounds, such as GA or ethylene, will modify the ABA:GA ratio removing dormancy effects,
allowing seed to germinate. This was confirmed by Borghetti et al. (2002), when seeds
submerged in ethrel (25 ppm) had significantly increased germination. Seiler (1994) reported
that the use of 1 mM solution of gibberelic acid (GA3) doubled the germination rate of dormant
sunflower seeds
Bratcher et al. 1993, successfully utilized tetrazolium chloride (TTC) to improve
germination of wild sunflower seeds. Treatments included perforating the seeds with a needle
and submerging the seeds in TTC. These physical mechanisms, or scarification, debilitate the
external structures or teguments facilitating water uptake and oxygen inflow.
12 CHAPTER III – Materials and Methods
Site description
This study was conducted at the Pioneer Hi-Bred facility located in Woodland, California
(UTM Zone 10 coordinates: E: 600939, N: 4281280), which is the main summer location for
sunflower research. Summers are hot with an average temperature of 35.8oC and winters are cold
with average minimum temperature of 3.1oC. Precipitation occurs almost exclusively between
November and March, with an average of 470 mm per year (Western Regional Climate Center,
2011). The soil is classified as Yolo Silt Loam by the Soil Survey of Yolo County (Andrews,
1972). This soil is a member of the Fine-silty, mixed, superactive, nonacid, thermic Mollic
Xerofluvents.
Material Selection
Materials to be tested were carefully selected based on potential dormancy effects.
Pioneer has an annual evaluation on all inbred lines comparing relative maturity. Six lines with
the longest maturities over the last three years were used in this study. Three of them are
characterized as high oleic materials, which are also known to exhibit dormancy. The following
inbreds were evaluated: conventional line 1 (L1), conventional line 2 (L2), conventional line 3
(L3), high Oleic line 1 (L4), high Oleic line 2 (L5), high Oleic line 3 (L6)
Foundation seed was produced at the Wiamea station located in Kekaha, Kauai, HI. The
seed was planted on January 31st, 2012. To be consistent across different maturities, each line
was harvested exactly 30 days after flowering. Once harvested, lines were kept in a cold room
(48°F and 45% RH) until shipped to Woodland, CA on May 27th, 2012 for the main study.
13 To determine a baseline and identify if seeds were dormant, a germination test was
performed in the laboratory under controlled conditions. A warm germination test was compared
to a cold germination test to evaluate possible dormancy effects. In the warm germination test,
50 seeds of each inbred were placed in a germ towel and sprayed with water. The towel was
folded to assure contact between seeds and then placed in a growth chamber at 25°C for seven
days. The percentages of normal, dormant and dead seed were calculated. The cold germination
test was the same as the warm test, but required a pre-chill of seven days at 10°C prior to the
seven days at 25°C. Exposure to the pre-chill technique greatly improved the germination rate in
these inbreds (Table 2). This evaluation under controlled conditions clearly revealed the presence
of dormancy problems in all lines. Once dormancy was confirmed, the main study was
conducted by testing four proven methods of breaking dormancy.
Table 2. Germination of six sunflower inbreds using warm and cold germination tests
Line
Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Germination under warm test
Germination under cold test
42%
39%
31%
34%
27%
37%
92%
92%
92%
94%
94%
94%
14 Experimental treatments
Seeds from each line were divided into five groups and exposed to the described
treatments using four replications (Table 3).
Temperature changes were used in the first treatment, in which seeds were exposed to 8
cycles of alternating temperatures: 30 minutes of -80°C followed by 30 minutes of room
temperature (20°C). These temperature changes promote minuscule fractures in the outside
layers of the seed, facilitating water imbibition and oxygen flow.
The second treatment was a mechanical cut on each seed to assure water uptake and
oxygen flow into the seed. Seed chipping was manually performed with dog nail clippers cutting
the tip of each hull without damaging the seed.
In the third treatment, seeds were enclosed in a chamber with a saturated atmosphere of
100% ethylene gas for 12 hours at 20°C; this treatment was intended to remove physiological
dormancy.
The fourth treatment was ethrel application in which seeds were submerged into a
solution of 30ppm ethrel (Ethepon 2SL diluted with water) for 15 minutes. This treatment
presoaks the seeds and triggers germination by increasing the GA concentration.
Table 3 List of treatments tested for breaking dormancy in sunflower inbreds.
Dormancy effect to act on
1- Physical limitation
2- Physical limitation
3- Physiological changes
4- Combination of 2 & 3
5- Control
Treatment
Freezing – Thawing cycles
Seed chipping
Ethylene exposure (gas)
Ethrel submersion (liquid)
No treatment
15 Action
+20°C to - 80°C
Mechanical cut on the hull
12hs @ saturated atmosphere
15 minutes
The last treatment in the experiment was the control, in which seeds were kept in the cold
room (9°C and 45% RH) during night and brought out during day (20°C) until planted. This is
the normal procedure the sunflower breeding program utilizes because seed needs to be weighted
and conditioned for packet filling.
Experimental design
A split plot randomized complete block design was utilized to establish the plots in the
field (Figure 4). There were six lines, and five dormancy treatments replicated four times
(blocks). Seed treatments were the main plots while the subplots consisted of the six sunflower
inbred lines.
L4
L5
L6
L3
L2
L4
L5
L6
L3
L2
L4
L5
L6
L3
L2
L4
L5
L6
L3
L2
3
L3
L6
L1
L4
L5
L3
L6
L1
L4
L5
L3
L6
L1
L4
L5
L3
L6
L1
L4
L5
4
L6
L4
L5
L1
L6
L6
L4
L5
L1
L6
L6
L4
L5
L1
L6
L6
L4
L5
L1
L6
5
L1
L2
L3
L5
L4
L1
L2
L3
L5
L4
L1
L2
L3
L5
L4
L1
L2
L3
L5
L4
6
Rep 1
L5
L3
L2
L6
L1
L5
L3
L2
L6
L1
L5
L3
L2
L6
L1
L5
L3
L2
L6
L1
2
Rep 2
L2
L1
L4
L2
L3
L2
L1
L4
L2
L3
L2
L1
L4
L2
L3
L2
L1
L4
L2
L3
1
Rep 3
Chip
Submer.
Control
Temp
Gas
Submer.
Gas
Temp
Control
Chip
Control
Gas
Chip
Temp
Submer.
Temp
Chip
Gas
Submer.
Control
Rep 4
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
Figure 4. Layout of research plots in the field using a split plot randomized
complete block design.
16 Before planting, the field was pre-irrigated with 25mm of water by drip irrigation and
sprayed with glyphosate to eliminate any emerging weeds. Soil temperature at planting depth
(2.5 cm) was 23°C. The experiment was planted on June 1st, 2012. The planter utilized was the
Almaco Seed Pro, which is specifically designed for research purposes and provides detailed
information such as planting depth, numbers of seeds planted and spacing. The average number
of seeds per plot was 50 and the spacing between plants was 17 cm.
Immediately after planting, 37mm of water was provided by drip irrigation to assure
water imbibition. Weather conditions were optimal through the entire germination process, with
an average day temperature of 28°C, with some highs of 38°C, and an average night temperature
of 19°C.
Data Collection
Observations were made between June 6th and June 27th, 2012. Number of emerged
plants per plot was recorded on a daily basis until 21 days after planting. After 21 days, very few
plants will emerge and flowering will be delayed, limiting the opportunity to make breeding
crosses. Germination was calculated as an absolute value; the plant was either emerged or not.
Fully expanded cotyledons was the threshold to determine that a plant had emerged.
Statistical Analysis
Data collected during the experiment were analyzed using Proc GLM in Statistical
Analysis Software (SAS). Data were analyzed as a split plot randomized complete block design.
The Ryan-Einot-Gabriel-Welsch multiple range test was utilized to determine if there were
significant differences among means.
17 CHAPTER IV – Results and Discussion
Based on the statistical analysis, there were significant (P < 0.0001) differences among
treatments (Table 4). Mean emergence of the control treatment was equivalent to emergence of
the temperature treatment and was significantly higher than the rest of the treatments (Table 5).
Mean germination was 54% for the control and 52% in seed that received the temperature
treatment. Seeds exposed to ethylene gas had a mean germination of 45%, which was the same
mean as those submerged in Ethrel. Seed chipping treatment had 32% germination, which was
significantly lower than all other treatments (Table 5).
Table 4. ANOVA table for percent emerged plants of dormant Sunflower inbreds.
Source of Variation
Degrees of
Freedom
Sum of
Squares
Mean Square
F Value
Pr > F
Block
3
1290.00
430.00
5.78
0.1001
Treatment
4
6953.80
1738.45
23.38
< 0.0001
Main Plot Error
12
892.33
74.36
0.37
0.9691
Inbred
5
13830.26
2766.05
13.88
< 0.0001
Treat * Inbred
20
8973.40
448.67
2.25
0.0062
Subplot Error
75
14949.66
199.32
Table 5. Germination percentage for each seed treatment.
Treatment
Control
Temperature
Gas exposure
Submersion
Chipping
Germination %
54a †
52ab
45b
45b
32c
† Means followed by the same letter are not significantly different (P<0.05)
using Ryan-Einot-Gabriel-Welsh
18 The statistical analysis also indicated that there was a significant interaction (P = 0.0062)
between treatments and inbreds (Table 4). Seed chipping improved germination for Line 1 from
a mean of 50% to 63%, while the same treatment negatively affected germination for Line 6
from a mean of 61% to 30% (Table 6). Line 6 had the highest germination rate across treatments,
but germination fell noticeably with seed chipping. This was also confirmed by Brunick (2007)
where achene excisions produce mixed results and germination varied with genotypes. The
control was the only treatment that showed consistent emergence compared to other treatments.
Germination across lines was also variable. The expectation that linoleic lines present
better germination compared to high oleic lines could not be confirmed. Two of the three linoleic
lines had germination rates above or equal to 50%. Germination percentage in high oleic lines
ranged from 30-37% except for line 6, which had 61% germination, the highest value in the
study (Table 6). The results are similar to the findings of Murcia et al. (2002). However, the
small set of inbreds tested is not sufficient to draw conclusions on germination rates between oil
profiles.
Table 6. Germination percentage by seed treatment and sunflower line.
Line1
Line2
Line3
Line4
Line5
Line6
Mean by treatment
§
Temperature
Seed
Chipping
Ethylene
gas
Ethrel
submersion
Control
Mean by line
43
54
64
46
32
73
§
52 63
33
36
16
15
30
32
47
24
49
40
43
69
45
47
32
63
36
31
61
45
51
43
73
46
42
70
54
50
37
57
37
33
61
For line means within treatments, LSD0.05 = 19.9
19 CHAPTER V – Conclusions
Although the average germination values in this study were low (30 to 60%), it is
important to note that the conditions imposed were skewed towards dormancy. Only late
materials, which require longer time to mature, were used in this study. These lines were
harvested 30 days after flowering, allowing just sufficient time to complete the physiological
cycle without drying naturally.
Based on the premises stated in the objectives and the inbred lines tested, none of the
seed treatments provided superior germination over the control. Also, the seed treatments require
additional steps and are more expensive.
The observed interaction between lines and treatments could be due to different types of
dormancies affecting each line. This interaction is a major drawback because it prevents the
utilization of a single treatment for all lines, adding complexity to the entire process.
20 Literature Cited
Andrews, W.F. 1972. Soil survey of Yolo County, California. USDA Soil Conservation Service,
Washington DC.
Baskin, J.M. and C. Baskin. 2004. A classification system for seed dormancy. Seed Science and
Research 14: 1-16.
Bratcher B. C., J. M. Dole, and J. C. Cole. 1993. Stratification improves seed germination of five
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