This study examined seed dormancy in sunflower (Helianthus annuus L.) and methods for its safe removal. The study found: 1) Sunflower seeds exhibited dormancy in the early stages of maturation, with germination increasing from 2% at 30 days after pollination to 16% at 40 days. 2) Naturally, dormancy dissipated between 30-40 days after harvest, with maximum germination of 98.5% at 60 days after harvest. 3) For removing dormancy, soaking seeds in water for 24 hours resulted in the highest germination of 82%, followed by dry heating at 80C for 10 minutes which achieved 81% germination.

1. Study on Occurrence and Safe Removal of Dormancy in Sunflower
(Helianthus annuus L.)
Pallavi H M, Rame Gowda, Shadakshari Y G* and Vishwanath K
Department of Seed Science and Technology,
University of Agricultural Sciences, GKVK, Bangalore - 65, Karnataka, India
*AICRP on Sunflower, University of Agricultural Sciences, GKVK, Bangalore - 65, Karnataka, India
e-mail: pallavihm@gmail.com
A B S T R A C T
A study was conducted on the seed maturation and occurrence of seed dormancy and safe removal
method using physical and chemical methods. The study showed that germination per cent was very low
(2.0%) at 30 days after pollination (DAP) and increased to 16% after 40 DAP. The dormancy dissipated
naturally between 30 to 40 days after harvest (DAH). Maximum germination was recorded at 60 DAH
(98.50%) followed by 50 DAH (96.75%). Besides, seed dormancy breaking study revealed that the seeds
soaked in water for 24 hours recorded higher germination (82%) followed by dry heating at 80°C for 10
minutes (81%). Seeds treated with GA3 @ 100 ppm recorded higher seedling vigour index (908) followed
by ethrel @ 25 ppm (904) and water (902). The smoke treatment with ‘sambrani’ also resulted in
significant improvement in germination (80%) over control (24%).
Key words: Sunflower, Seed dormancy, Seed treatments, Seed maturation
Dormancy is an important component of
physiological quality of sunflower seeds. Presence of
dormancy causes germination problems in sunflower
seeds since it delays the embryo growth and
development and is controlled by endogenous action of
seeds (Amen 1968). Sunflower require 40-45 days to
attain germination capacity, thereby delays the
immediate sowing of the seeds for seed and commercial
production. Further, dormancy increases when
germination takes place under stress (poor field
conditions).
Dormancy is reported to be innate and is the
resultant of interaction between maternal and
embryonic genotypes (Zimmerman and Zimmer 1978).
Bianco et al. (1994) studied the occurrence of dormancy
and found that period of dormancy varied between
cultivars ranging from 12 to 40 days after maturity. The
degree of maturity of the seeds also influence the
dormancy duration. It has reported that seeds harvested
early with moisture content of 41-62 per cent showed
dormancy for 42-50 days while, seeds harvested at the
final maturity stage with moisture content 8-12 per cent
possess dormancy only for 22-29 days after harvesting.
It has to be safely removed before planting seeds to
obtain uniform and better germination. The embryos of
sunflower are capable of germinating after 12-16 DAA
followed by deep dormancy at 20-30 DAA due to
accumulation of Abscisic acid (Le Page et al. 1996) and
presence of thick pericarp and seed coat
(Subrahmanyam et al. 2002). However, the embryos
gained germination capacity at 40 DAA (Ramazunova
1994). At the time of maturity, the balance in promoter-
inhibitor is more towards inhibitors, thus imposing
dormancy. However, dormant mature seeds of
sunflower will eliminate dormancy during storage in
under conditions.
Seiler (1993) reported that the age of achenes at
harvest of wild Helianthus annuus and H. petiolaris had
a significant influence on germination and the
maximum germination took place by 21 DAA, while,
combination of storage temperatures and time could not
break dormancy. Further, stated (Singh and Rao 1994)
that chemical pre-treatment of wild sunflower achenes
with 1mM solution of gibberellic acid (GA3) almost
doubled the germination percentage over a non-treated
control. The age of the achenes at harvest influenced the
germination. Achenes of H. petiolaris, harvested 20
DAF generally had greater germination than those
harvested at 40 DAF. Germination of GA3 treated seeds
was 81 per cent compared with 38 per cent in control
and the enhanced germination was regardless of achene
maturity, storage time or storage temperature (Gerald
1998). Seed dormancy of wild sunflowers (H. annuus,
H. argophyllus and H. exilis) was found to be controlled
primarily by the seed covering (seed coat and pericarp)
and embryo dormancy was short-lived (four to eight
weeks).
Ethylene and its precursor known to enhance the
germination by breaking dormancy (Corbineau et al.
1990). The protease activity may be involved in the
removal of dormancy by ethylene and the improvement
of germination of the sunflower embryo (Borghetti et
al. 2002). Since sunflower seeds exhibits 45 to 60 days
of dormancy after harvesting, there is a need to identify
a simple low cost technique for its safe removal.
Several researchers have made an attempt to develop a
chemical seed treatment technique for the safe removal
of dormancy and succeeded in it. Singh and Rao (1994)
Research Journal of Agricultural Sciences 2010, 1(4): 341-344
341

2. also observed that sunflower parental lines, soaked with
GA3 recorded in higher germination, however, the
MSCS of 70 per cent germination was obtained by
soaking in water for 24 hours. Maiti et al. (2005)
indicated that sunflower genotypes showed a large
variability in dormancy. In general, sunflower hybrids
showed greater levels of seed dormancy than the
cultivated genotypes. Seed germination was highest
under alternating conditions of 12 hours light and 12
hours darkness.
The dormancy is mainly due to embryo dormancy
and disappears during dry storage in sunflower (Oracz
et al. 2008). Endogenous ethylene is involved in
sunflower seed alleviation of dormancy. Cyanide is
produced during the conversion of 1-
aminocyclopropane 1-carboxylic acid to ethylene.
While naked dormant sunflower seeds germinated at
10°C when incubated in the presence of 1mM gaseous
cyanide. Cyanide stimulated germination of dormant
seeds in the presence of inhibitors of ethylene
biosynthesis, but its improving effect required
functional ethylene receptors. This has not affected
ethylene production and the expression of genes
involved in ethylene biosynthesis or in the first steps of
ethylene signaling pathway. However, the expression of
the transcription factor ethylene response factor 1
(ERF1) was markedly stimulated in the presence of
gaseous cyanide.
The dormancy of the sunflower was overcome by
soaking seeds in etherel (25ppm) (Borghetti et al. 2002)
and also through hydro priming (Maiti et al. 2005). The
physical treatments which does not involve water as a
component was under significance to ease the dormancy
breaking treatments while handling large mass of seeds
at a time. While handling large bulk of seeds, soaking in
water is risky since it needs to redry seeds to its original
moisture content before packing and shifting. Keeping
the above in view is essential to develop a suitable
technique which eliminates soaking of seeds in water.
MATERIALS AND METHODS
Test weight of sunflower seeds recorded at
different stages of maturity differed significantly.
Maximum seed weight (5.597g) was recorded in seeds
harvested at 30 days after pollination (DAP) which was
on par with the seeds harvested at 40 DAP (5.567g).
Lower dry matter accumulation was observed when
seeds harvested at 10 DAP (1.324g). The seed weight
increased as the days to maturity increased might be due
to the accumulation of food reserves in the cotyledons.
Sunflower being an oil seed crop the accumulation of
oil in the seed increased only after 10 DAP
correspondingly resulted in increased seed weight. The
germination of sunflower seeds harvested at 10 DAP
was zero and there was no germination till the seeds
attained the maximum dry weight (30 DAP). The
germination was only 2.0 per cent when harvested at 30
DAP and increased to 18.0 per cent after 40 DAP. The
accumulation of food reserves have direct relationship
with the germination per cent
Table 1 Influence of maturity stages on 100 seed
weight (g) and germination (%) in
sunflower hybrid KBSH-44
Maturity stages 100 seed
weight (g)
Germination
(%)
10 DAP 1.324 0.00
20 DAP 3.275 0.00
30 DAP 5.597 1.00
40 DAP 5.567 16.0
Mean 3.888 5.00
S. Em± 0.062 -
CD (0.05P) 0.13 -
CV (%) 2.50 -
Freshly harvested matured seeds of sunflower
hybrid KBSH-44 were tested for its germination from
date of harvest and at weekly interval to check its
natural dissipation of dormancy (Table 2). Freshly
harvested seeds recorded zero per cent germination. The
germination per cent has increased from 0 DAH to 60
DAH. There was gradual decrease in per cent dormancy
and increase in germination per cent. Seeds attained
maximum germination (100%) at 60 DAH followed by
50 DAH (97.0%). Sunflower requires 40-45 days to
attain full germination capacity, thereby delays the
immediate sowing of the seeds for commercial crop
production. This confirmed the presence of dormancy in
freshly harvested seeds of sunflower. However, the
seeds attained 85.5 per cent of germination at 40 DAH
which is more than the MSCS. Thus, the seeds of
sunflower could be safely used for sowing after 30 to 40
days after harvest. However, complete elimination of
dormancy was observed only after 60 DAH. The
dormancy in sunflower is mainly due to under
developed embryo and disappears during dry storage in
sunflower (Oracz et al. 2008). Harvest dormancy of
sunflower seeds can be released by after-ripening and
involves hormonal changes like decrease in ABA
biosynthesis and sensitivity (Corbineau et al. 1990, Le
Page et al.1992, Le Page et al. 1996). Dry storage of
mature or immature seeds strongly improves
germination by breaking embryo dormancy and seed
coat inhibition (Corbineau et al.1989).
RESULTS AND DISCUSSION
Safe removal of seed dormancy
Freshly harvested seeds of sunflower were treated
with different physical and chemical treatments for its
safe removal of dormancy and the results are presented
in Table 3.
Viability (%)
The per cent seed viability varied significantly after
physical and chemical seed treatments imposed to break
the dormancy. Viability decreased significantly when
342
Pallavi et al.

3. the seeds were dry heated at high temperatures. Among
the different treatments, lowest per cent of viability was
recorded when seeds were dry heated at 100°C for 5
minutes (T10-19%) followed by micro wave exposure
for 60 seconds (T16-26%). The reduced activity of
dehydrogenase might have caused seeds to become
nonviable. Seeds treated with chemicals did not show
any reduction in viability per cent. However, highest
(99%) was recorded in seeds treated with Ethrel (25
ppm), thiourea (100 ppm) and KNO3 (2%) followed by
chemically treated seeds.
Table 2 Natural dissipation of seed dormancy in
sunflower hybrid KBSH-44
Days after
harvest
R1 R2 R3 R4 Mean
0 7 5 8 6 6.50
7 16 24 18 22 20.00
14 34 32 33 36 33.75
20 36 32 38 36 35.50
30 59 62 58 64 60.75
40 85 86 88 84 85.75
50 96 98 96 97 96.75
60 100 100 98 96 98.50
Mean 54.13 54.88 54.63 55.13
Germination (%)
The influence of various dormancy breaking
methods on germination percentage varied significantly.
In general seeds treated with chemicals recorded higher
germination when compared to physical treatments.
Among the treatments, seeds soaked in water for 24
hours recorded maximum germination (82 %) followed
by dry heating at 80°C for 10 minutes (81%), Ethrel @
25 ppm (80 %), smoke for 3h (80%) and GA3 @ 100
ppm (79 %) as against the control where it was only 24
per cent. Similar results have been reported by (Singh
and Rao 1994, Gerald 1998, Borghetti et al. 2002,
Fabian et al. 2002) opined that the protease activity
might be involved in breaking dormancy by ethylene
and there by improvement in germination of sunflower
embryo was seen. The causal mechanism of breaking
dormancy/ enhancing germination induced by chemical
treatments might be due to some chemical changes in
the seed during the change from solution to gel stage by
soaking and drying process. This might be associated
with the washing away of the inhibitor, ABA and
further during the process, the porosity of the seed coat
might have increased and resulted in increased
germination per cent (Maiti et al. 2005). The increased
germination in dry heat treatments could be due to the
denaturation of inhibitors and also enhanced after
ripening process.
Table 3 Influence of different physical and chemical seed treatments on seed quality parameters and release of
dormancy in sunflower hybrid (KBSH-44)
Treatments Viability
(%)
Germination
(%)
% increase
over control
Seedling dry
weight (mg)
SVI
T1: Control 96 24 --- 11.50 276
T2: Water (24 hrs) 98 82 241.6 11.00 902
T3: Dry heating (60°C,15 min) 54 54 125.0 11.40 615
T4: Dry heating (60° C, 30 min) 55 50 108.3 09.50 475
T5: Dry heating (60° C, 60 min) 47 46 91.66 09.15 420
T6: Dry heating (70°C, 15 min) 49 48 100.0 10.85 520
T7: Dry heating (70°C, 30 min) 48 47 95.83 07.55 354
T8: Dry heating (80° C, 15 min) 46 43 79.16 10.10 434
T9: Dry heating (80°C, 10 min) 87 81 237.5 08.75 708
T10: Dry heating (100° C, 5 min) 19 15 -37.50 08.15 122
T11: Dry heating (100° C, 2 min) 50 50 108.3 09.20 460
T12: Microwave (80%, 30 sec.) 55 55 129.1 09.30 511
T13: Microwave (80%, 60 sec.) 43 43 79.16 09.05 389
T14: Microwave (100%, 20 sec.) 46 45 87.50 10.85 488
T15: Microwave (100%, 30 sec.) 35 34 41.66 7.70 261
T16: Microwave (100%, 60 sec.) 26 26 8.333 5.10 132
T17: Smoking (3 hours) 97 80 233.3 10.50 840
T18: GA3 (100 ppm) 98 79 229.1 11.50 908
T19: Thiourea (100 ppm) 99 66 175.0 09.50 532
T20: Ethrel (25 ppm) 99 80 233.3 11.30 904
T21: KNO3 (2%) 99 76 216.6 11.00 836
Mean 64.09 52.19 - 10.14 520.56
S.Em± 1.90 4.58 - 0.989 74.36
CD (0.05P) 3.96 9.54 - 2.058 154.64
CV (%) 3.32 3.5 - 2.6 4.48
343
Study on Occurrence and Safe Removal of Dormancy in Sunflower

4. Seedling dry weight (mg) and Seedling vigour index
The mean seedling dry weight differed significantly
due to dormancy breaking treatments. The seeds treated
with GA3 @ 100 ppm recorded higher seedling dry
weight (11.50mg) and it was lower in micro wave
exposure for 60 sec (5.10mg). Though the seeds dry
heated at 80°C had recorded higher germination (81%),
the seedling dry weight was lower (8.75mg) due to the
shortened seedling length. Similarly, higher seedling
vigour index was recorded when seeds were treated
with GA3 @ 100 ppm (908) followed by ethrel 25 ppm
(904) and water (902). However, the seedling vigour
index was greatly affected in dry heat at 100°C for 5
minutes (122) followed by microwave exposure for 60
seconds (132). When seeds exposed to high energy
treatments might have affected the enzyme activation
resulting in reduced seedling growth and vigour index.
Seeds exposed to sambrani smoke for 3 hours had
also stimulated germination (80%), better seedling dry
weight (10.5mg) and vigour (840) compared to control.
Tieu et al. (2001) opined that ethylene in the smoke was
responsible for the stimulation of germination (Brown
and Staden 1997). Thus both smoke treatment and
drying treatments can be commonly exploited for
removal of seed dormancy in sunflower. However, the
protocol needs to be refined further.
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