Utilization of diverse rice ecotypes in heterosis breeding

A classification based on RFLP markers and morphological trait index was conducted in four photoperiod- and/or thermo-sensitive genic male sterile rice (PGMS or TGMS) lines and 49 rice varieties of nine different ecotypic origins. The results indicated that the combination of the two classification methods enabled to classify clearly and similarly the materials into two groups, indica and japonica. The 49 varieties were test-crossed to the four PGMS or TGMS lines used as female parents. Grain yield of the test-crossed F₁s of diverse ecotypes exhibited remarkable differences, especially in three parameters, i.e. number of combinations over a check, extent of standard heterosis and heterobeltiosis. In general, the first two showed higher values in indica-japonica crosses than in crosses between two different ecotypes within the same subspecies. For each female parent except for LS2S, there were corresponding optimum ecotypes of male parents. In terms of grain yield advantages and above-mentioned parameters, patterns of heterotic combinations were as follows: Peiai64S in combination with japonica varieties of northeastern China, restorers of japonica rice hybrids, or japonica varieties of North China; N422S in combination with indica varieties of China, indica varieties of Korea; 108S with American new varieties, japonica varieties of northeastern China, and indica varieties of China. LS2S showed a lower general combining ability.