Estimates of combining ability for cold tolerance at reproductive stage in rice

Ninety F₁ rice hybrids, produced by crossing 15 rice cultivars having lowtemperature tolerance at different growth stages with 6 high yielding elite IRRI cultivars, were evaluated for combining ability for reproductive stage cold tolerance. Evaluation was done by subjecting the plants to 17℃ and 20℃ water temperatures, in separate blocks, from 20 days after transplanting to maturity. Both general (GCA) and specific (SCA) combining ability variances were significant, with estimates of GCA being larger for all traits, showing predominance of additive type of gene action. The indica parents viz. Samgangbyeo, Suweon 287, Shoa-Nan-Tsan, K 39-96, China 988, IR 9202, Leng Kwang, IR 7167 and IR 15889 proved to be good donors for reproductive stage cold tolerance. Parental performance per se was a good indicator of general combining ability effects of the parents, but no association was observed between per se performance of the crosses and their specific combining ability effects.