Genetic Control of Seed Dormancy in Basmati Rice

Abstract

Seed dormancy in rice (Oryza sativa L.) is important to avoid losses due to germination rains during harvesting. Four indica type rice cultivars (Basmati 370, Type 3, P2 and PR106), as well as F 3 seeds obtained from a cross of Basmati Type3 with seed dormancy and non-dormant and non-basmati P2, were used to investigate the genetic control of seed dormancy at different temperatures and days after harvesting (DAH). The seeds of non-basmati rice cultivars germinated immediately after harvesting, while seeds of the traditional Basmati cultivars, Basmati 370 and Type 3 remained dormant. Seed dormancy in Basmati cultivars was hull-imposed, and could not be overcome by the usual heat treatment of seeds at 45 0 C for 72. Both the Basmati cultivars continued to have a dormant seeds up to 50 DAH. The F 3 seeds from 160 F 2 plants from a cross of Basmati Type 3 with non-Basmati P2 were investigated for genetics of seed dormancy. The F 3 seeds of F 2 plants segregated for dormant: non-dormant seeds at 50 DAH at room temperature in 13:3 ratio, suggesting that two genes one dominant and another recessive controlled seed dormancy in Basmati cultivars. For heat-treated seeds at 50 DAH, a 1:3 ratio of dormant: non-dormant F 2 plant/F 3 seeds was observed and this response ratio was maintained up to 100 DAH without heat treatment, indicating the long term effectiveness of the recessive gene controlling the seed dormancy. The dormancy conditioned by the dominant gene was overcome by heat treatment whereas the part controlled by the recessive gene continued to be effective. Seed dormancy is defined as the temporary inability of a viable seed to germinate upto a specific period of time under favourable conditions. This is an adaptive trait that promotes the survival of many plants in nature (Simpson, 1990). There are two ways by which seed dormancy is imposed: seed coverings (e.g. pericarp, testa and in some cases the endosperm) and in other cases the embryo itself (Bewley and Black, 1994). A dormant seed would continue its state until a specific environment overcomes its dormancy (Simpson, 1990) and this condition is known as after-ripening seed dormancy. In general, freshly harvested seeds of indica rice cultivar are dormant while that of japonica rice cultivars are non-dormant (Hartman et al., 1997; Ellis et al., 1983). Seed dormancy in wild species has been found to be primitive trait of rice (Takahashi, 1984) which was lost during domestication. Vearsey et al., (2004) found lower intensity of seed dormancy of the cultivated species of rice compared to its wild species. Seed dormancy is common in grasses like Hordeum vulgare, Avena spp., Secale cereale (Simpson, 1990). The QTLs (quantitative trait loci) associated with pre-harvest sprouting resistance genes have been identified in barley (Prada et al., 2004), sorghum (Lijavetzky et al., 2000) and wheat (Kulwal et al., 2004). The QTLs controlling seed

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*Corresponding author email : hsdhaliwal07@gmail.com,
Madras Agric. J., 96 (7-12): 305-308, December 2009
Genetic Control of Seed Dormancy in Basmati Rice
M. Kumar1, D. Rajpurohit1, P.O. Basha1, A. Bhalla, G.S. Randhawa and H.S. Dhaliwal*
1Contributed equally to the paper, Department of Biotechnology,
Indian Institute of Technology, Roorkee-247 667, Uttarakhand
Seed dormancy in rice (Oryza sativa L.) is important to avoid losses due to germination rains
during harvesting. Four indica type rice cultivars (Basmati 370, Type 3, P2 and PR106), as well
as F3 seeds obtained from a cross of Basmati Type3 with seed dormancy and non-dormant
and non-basmati P2, were used to investigate the genetic control of seed dormancy at different
temperatures and days after harvesting (DAH). The seeds of non-basmati rice cultivars
germinated immediately after harvesting, while seeds of the traditional Basmati cultivars,
Basmati 370 and Type 3 remained dormant. Seed dormancy in Basmati cultivars was hull-
imposed, and could not be overcome by the usual heat treatment of seeds at 450C for 72. Both
the Basmati cultivars continued to have a dormant seeds up to 50 DAH. The F3 seeds from 160
F2 plants from a cross of Basmati Type 3 with non-Basmati P2 were investigated for genetics
of seed dormancy. The F3 seeds of F2 plants segregated for dormant: non-dormant seeds at
50 DAH at room temperature in 13:3 ratio, suggesting that two genes one dominant and
another recessive controlled seed dormancy in Basmati cultivars. For heat-treated seeds at
50 DAH, a 1:3 ratio of dormant: non-dormant F2 plant/F3 seeds was observed and this response
ratio was maintained up to 100 DAH without heat treatment, indicating the long term
effectiveness of the recessive gene controlling the seed dormancy. The dormancy conditioned
by the dominant gene was overcome by heat treatment whereas the part controlled by the
recessive gene continued to be effective.
Key words: Oryza sativa, basmati rice, germination, heat treatment, seed dormancy
Seed dormancy is defined as the temporary
inability of a viable seed to germinate upto a specific
period of time under favourable conditions. This is
an adaptive trait that promotes the survival of many
plants in nature (Simpson, 1990). There are two
ways by which seed dormancy is imposed: seed
coverings (e.g. pericarp, testa and in some cases
the endosperm) and in other cases the embryo itself
(Bewley and Black, 1994). A dormant seed would
continue its state until a specific environment
overcomes its dormancy (Simpson, 1990) and this
condition is known as after-ripening seed dormancy.
In general, freshly harvested seeds of indica rice
cultivar are dormant while that of japonica rice
cultivars are non-dormant (Hartman et al., 1997; Ellis
et al., 1983).
Seed dormancy in wild species has been found
to be primitive trait of rice (Takahashi, 1984) which
was lost during domestication. Vearsey et al., (2004)
found lower intensity of seed dormancy of the
cultivated species of rice compared to its wild
species. Seed dormancy is common in grasses
like Hordeum vulgare, Avena spp., Secale cereale
(Simpson, 1990). The QTLs (quantitative trait loci)
associated with pre-harvest sprouting resistance
genes have been identified in barley (Prada et al.,
2004), sorghum (Lijavetzky et al., 2000) and wheat
(Kulwal et al., 2004). The QTLs controlling seed
dormancy have been reported in cultivated O. sativa
(Dong et al., 2002; Miura et al., 2002; Wan et al.,
1997), in wild rice, O. rufipogon (Cai and Morishima,
2000) and in weedy rice, O.sativa (Gu et al., 2004).
Self-sown Basmati rice plants were observed in
the wheat experimental material in March, 2005 in
the field plots at the Indian Institute of Technology,
Roorkee, where two traditional Basmati cultivars
Type3 and Basmati 370 were grown from July to
October, 2004. The plants from the self-sown seeds
were tall, photosensitive and had typical grain
characteristics similar to that of Type 3 and Basmati
370, suggesting that the basmati cultivars had strong
after-ripening seed dormancy up to 100 days under
low temperature (4-25ºC) field condition in winter.
This article deals with the study of genetics of seed
dormancy in a traditional Basmati rice cultivar Type 3.
Materials and Methods
The plant material consisting of two traditional
Basmati cultivars, Basmati 370 and Dehraduni
Basmati (Type 3) and non basmati indica rice
cultivars were obtained from the Punjab Agricultural
University, Ludhiana.
Hulled and dehulled seeds of freshly harvested
grains of two traditional Basmati cultivars, Basmati
370 and Type 3 and two non-basmati semi-dwarf

306
indica rice cultivars PR106 and P2 (PR106 with
bacterial leaf blight resistance genes xa5, xa13 and
Xa21 pyramided) were harvested and threshed
gently by hand. The harvested seeds were tested
for germination 10 days after harvesting (DAH) in
Petri plates at room temperature with and without
heat treatment. For breaking the seed dormancy,
the hulled grains were treated at 45ºC for 72 h. The
hulled grains were tested for germination at room
temperature (25ºC) with and without heat treatment
at 15, 40, 50 and 100 DAH.
To study the genetics of seed dormancy, 160 F3
progenies (seeds obtained from the F2 plants) from
a cross of Basmati Type 3 with dormant seeds and
non-dormant and non-basmati P2 indica rice
cultivars were tested for germination at 50 DAH and
100 DAH with and without heat treatment. Different
germination percentage cut-off points were taken to
classify the dormant vs. non-dormant progenies
depending upon the parental seed germination
under different conditions.
Self-sown Basmati370/Type 3 0 0 0 60 10 15 45 60
Basmati 370 0 0 0 70 20 30 50 70
Type 3 0 0 5 60 10 20 45 60
P2 70 80 80 95 75 85 95 100
PR106 70 75 85 100 70 85 90 100
15 DAH 40 DAH 50 DAH 100 DAH 15 DAH 40 DAH 50 DAH 100 DAH
Rice Cultivars Germination % without heat treatment Germination % after heat treatment
Table 2. Germination of hulled seeds of self-sown Basmati 370/Type 3, traditional basmati and non-
basmati rice cultivars at different DAH
Table1. Germination of hulled and dehulled seeds
of traditional basmati and non-basmati indica rice
cultivars with and without heat treatment
Basmati 370 12 95 32 95
Type 3 16 85 26 85
P2 76 86 92 90
PR106 85 90 80 90
With
Hull
Cultivar Germination %
without heat
treatment at 10 DAH
Germination %
with heat treatment
at 10 DAH
Without
Hull With
Hull Without
Hull
Seed germination of non-dormant cultivars PR
106 and its near isogenic line P2 improved steadily
from 70% (15 DAH), 85% (50 DAH) to above 90%
(100 DAH) whereas the seed of self-sown Basmati
370/Type 3, Basmati 370 and Type 3 had no
germination till 50 DAH (Table 2). The heat treatment
of hulled seed could only slightly enhance
germination from 0-20% (15 DAH), and 50% (50
DAH) and not overcome completely. The maximum
germination of Basmati cultivars with and without
heat treatment was 60-70% even at 100 DAH. Lower
seed germination (<70%) in basmati cultivars even
after heat treatment at 100 DAH indicated the
presence of residual dormancy which is not
overcome by the recommended heat treatment.
The frequency distribution of germination of
different F3 seeds under three different germination
conditions is given in Figure 1. Considering that the
Type 3 seeds would start germinating between 50-
100 DAH and by taking 35% germination as the cut-
off point between dormant and non-dormant F3
seeds at 50 DAH, the F2 plants segregated into 129
dormant: 31 non-dormant in 13:3 ratio (χ2 = 0.041,
P<0.05) (Fig. 1a), indicating that the hull imposed
seed dormancy is controlled by two genes, one
dominant and the other recessive. Shenoy (1993)
in his study on the genetics of hull imposed
dormancy in rice seeds, obtained 9:7 ratio between
dormant vs. non dormant seeds upon fixing 80%
germination cut-off. After heat treatment at 50 DAH,
the majority of the progenies had above 50%
germination, the maximum germination of Basmati
370 after heat treatment at 50 DAH. The progenies
segregated in a ratio of 36 dormant to 124 non-
dormant progenies in 1:3 ratio (χ2 =0.53, P<0.05)
(Fig.1b), suggesting that a recessive gene controlled
residual dormancy. The dormancy conditioned by
the dominant gene was overcome by heat treatment,
whereas the part controlled by the recessive gene
continued to be expressed.
The germination of Type 3 at 100 DAH without
heat treatment was over 60%. Taking 65%
germination as the cut-off point between partially
dormant: non-dormant progenies at 100 DAH without
heat treatment, there were 43 dormant and 114 non-
dormant progenies which segregated in 1:3 (c2
=0.477, P<0.05) (Fig.1c) ratio, confirming that a
recessive gene in Type 3 still controlled partial
dormancy even 100 DAH and that this residual
dormancy could not be overcome by heat treatment.
It probably would require still longer heat treatment
Results and Discussion
Germination of PR106 and P2 with and without
hulls at 10 DAH with heat and without heat treatment
was 76-90%, indicating that there was little seed
dormancy in these non-basmati cultivars. In both
the traditional basmati cultivars, the germination of
hulled seeds was 12 and 16% without heat
treatment and 32 and 26% with heat treatment,
respectively, indicating that the recommended heat
treatment could break the dormancy only partially
and not completely (Table1). However, there was
80-90% seed germination in basmati and non-
basmati without hulls, irrespective of the heat
treatment, indicating that the hull imposed seed
dormancy upon traditional basmati cultivars to a
major extent. The hull-conditioned dormancy could
not be effectively overcome by the recommended
heat treatment.

307
Figure 1. Frequency distributions of seed germination of 160 F3 progenies of Type3 Basmati/P2 cross at 50
and 100 DAH. The black arrows denote the germination levels of the parents. Cut-off points between dormant
and non-dormant seeds in all three conditions have been marked by vertical arrow lines. Approximate
proportion of dormant and non-dormant progenies in each condition has been shown in parentheses. a. 50
DAH without heat treatment, b. 50 DAH after heat treatment. c. 100 DAH without heat treatment.
81
24
15
96855421
0
10
20
30
40
50
60
70
80
90
0 102030405060708090100
Germination percentage
No.of progenies
Typ e 3
P2
Dormant (13) Non Dormant (3)
(a)
Cut-off
4
1
7
5
8
11 11
19
28
30
36
0
5
10
15
20
25
30
35
40
0 102030405060708090100
Germination percentage
No . of pro genies
P2
Type 3
Dormant (1) Non Dormant (3)
(b)
Cut-off
1
45
2
8
5
18
30 31
38
15
0
5
10
15
20
25
30
35
40
0 102030405060708090100
Germination percentage
No.of progenies
Type 3
P2
Dormant (1) Non-dormant (3)
(c)
Cut-off
Fig 1a.
Fig 1b.
Fig 1c.
No. of progenies No. of progenies No. of progenies
Germination percentage
Germination percentage
Germination percentage

308
or additional time for restoring complete
germination. Das (1985), in his study on the genetics
of dormancy in rice, also found an epistatic (13:3)
and 3:1 ratio of dormant vs non-dormant seeds at 5
DAH and 35 DAH, respectively. Takahashi (1962)
found complementary dominant gene interaction for
seed dormancy in certain rice cultivars. Gu et al.
(2003) found the ratio of the low and high
germination plants in weedy and non-weedy rice
crop as 9:7, suggesting a digenic model for
controlling seed dormancy. Seed dormancy is
reported to be controlled by several QTLs.
From the results of this investigation, it can be
concluded that seed dormancy of traditional basmati
cultivars, Basmati 370 and Type 3 (Dehraduni
basmati) is imposed by hull and controlled by the
interaction of at least one dominant and one
recessive gene. The effect of the dominant gene
could be overcome by heat treatment, whereas the
one controlled by recessive gene resisted the heat
treatment and continued for much longer time. The
hull imposed seed dormancy in traditional Basmati
cultivars probably provided protection against
preharvest sprouting as the photosensitive
traditional basmati were adapted for cultivation in
flood prone low lying areas of Northern India. The
tagging and transfer of seed dormancy genes will
be useful for marker assisted selection in non-
basmati cultivars to avoid losses due to rain and
lodging during harvesting.
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Received: January 12, 2009; Revised: September 11, 2009; Accepted: November 10, 2009