Biotechnology Program, Directorate of Rice Research Rajendranagar, Hyderabad, AP, 500 030 India
Seed dormancy in rice has been attributed to both embryo and hull factors (Seshu and Sorrells 1986). Although there are several reports on the inheritance of seed dormancy per se in rice, few have attempted the analysis of inheritance of its components, viz., embryo and hull factors (Tomar 1984; Das 1985). In view of this, a study was taken up to investigate the genetics of hull-imposed dormancy by analyzing an F\2\ population of a cross between dormant cultivar Dular and non-dormant cultivar PTB1O.
Seed-lots with hull and without hull (dehulled) of the non-dormant parent PTB1O, showed more than 80% germination 20 days after harvest (DAH), when tested at 30degC for 7 days. In contrast, germination of the seeds with hull of the dormant parent Dular did not exceed 70% even after 60 DAH. Its dehulled seeds showed more than 80% germination at 10 DAH, suggesting that the dormancy is hull-imposed (Table 1).
Table 1. Seed germination patterns of dormant (Dular) and non-dormant (PTB1O) cultivars
======================================================================== Cultivar Condition % germination/Days after harvest (DAH) DAH: 10 20 30 40 50 60 ======================================================================== Dular Dehulled 95 96 100 With hull 17 28 31 54 58 70 PTBIO Dehulled 78 90 100 With hull 69 81 90 89 97 99 ========================================================================
Seed-lots showing more than 80% germination were considered non- dormant. The dehulled seeds of the parents and F\1\ plants at 30 DAH showed no dormancy, while the seeds with hull of the dormant parent and F\1\ showed dormancy. This suggests that the dormancy at 30 DAH was due to the hull factor only. To estimate the proportion of dormant to non-dormant plants in the F\2\, germination tests were conducted with 30 DAH seeds with hull.
Among the 300 F\2\ plants tested for germination at 30 DAH with hull, 173 were dormant and 127 non-dormant. Although the seeds from F\2\ plants represent F\3\ generation, the hulls belong to the mother plant and its genotype is the same as the F\2\ plant. The F\2\ ratio was assumed to be 9:7, which showed a good fit with the observed ratio (Table 2).
Table2. Segregation for seed dormancy in an F\2\ from cross DularxPTB1O
========================================================================= Class No. of seed-lots Total Chi-square Probability Dormant Non-dormant ========================================================================= Observed 173 123 300 0.19 0.75-0.50 (df = 1) Expected (9:7) 168.8 131.2 300 =========================================================================
Help rendered by Drs. D.V. Seshu and V. Krishnasami in providing facilities and generating the materials is gratefully acknowledged.
Das, R.C. 1985. Role of hull in inheritance of seed dormancy in rice. Exptl. Genetics 1(2): 119-125.
Seshu, D.V. and M.E. Sorrells. 1986. Genetic studies on seed dormancy in rice. IRRI (ed.), Rice Genetics, pp: 269-382.
Takahashi, N. 1962. Physicogenetical studies on germination of rice seeds with special reference to the genetical factors governing germination. Bull. Inst. Agr. Tohoku Univ. 14(l): 1-87. (in RGN 8: 35)
Tomar, J.B. 1984. Genetics of grain dormancy in rice (Oryza sativa L.). Genetica Agreria 38(4): 443-446.