DIALLEL ANALYSIS OF TILLER NUMBER AT DIFFERENT GROWTH-STAGES IN RICE (ORYZA-SATIVA L)

The genetics of tiller number at different development stages in rice was studied in a 6 x 6 diallel cross set involving six indica rice varieties in which a large difference of phenotypes existed. Estimates of genetic parameters following Hayman's method showed significant additive and nonadditive gene action, and the latter appeared to be solely due to dominance. High tillering ability was inherited as a partial dominant character conditioned by two or more blocks of genes, and var 'H1459' had more dominant genes, whereas 'Zhu-Yun-Luo' had more recessive ones. Combining ability analysis by Griffing's method also indicated significance of both additive and nonadditive effects, but the former was more important than the latter. 'H1459' and 'Bi-Yu-Zao-Luo' were good general combiners, and their hybrids 'H1459' x 'Le-Yi' and 'Zhu-Yun-Luo' x 'Bi-Yu-Zao-Luo' were better crosses for combining an optimum tiller number with high percentage of productive tiller. An identical polygenic system appeared to be responsible for the genetic control of both tiller number at the different growth stages and the terminal character, productive tiller number. However, with growth of the plant, relative contributions of nonadditive gene action and environmental factors to the variation decreased, while those of additive gene action increased. Selection for high tillering ability, therefore, should be exercised at peak tillering or later stages.