Heterosis of Biomass among Rice Ecospecies and Isozyme Polymorphism and RFLP.

Abstract

This experiment was carried out to study the relationship between heterosis and the polymorphism of genetic markers in rice. We employed 14 varieties, 4 japonica, 4 javanica and 6 indica. Of all the 91 possible combination, one indica × indica cross was missing, so 90 F1 cross combinations were used for half diallel analysis. They were transplanted in a field at 40 × 60 cm spacing and the top part of the plants was sampled and dried 43 days after transplanting to examine the degree of heterosis of biomass. The diallel analysis of the heterosis of biomass showed that dominant effect was larger than additive effect, suggesting that heterosis was contributed by the accumulation of dominant genes. More than 10 genes were considered to be involved in the heterosis. The general combining abiliy of biomass was highly significant and the heterosis of hybrids from crosses between indica and japonica varieties were generally large. Significant relationships were observed between the heterosis of biomass and the polymorphism of the 10 isozymes as well as 29 RFLP markers. However, the correlation coefficients were not so high. It seemed to be difficult to use the polymorphism of markers as an index of heterosis. The analysis of each marker and heterosis showed that several markers which were located dispersedly over the chromosomes showed significant correlations with the heterosis of biomass. According to the diallel analysis, more than 10 genes were related to the heterosis of biomass. Hybrids between indica varieties which have biomass controlled by dominant genes and japonica varieties which show over-dominance in crosses with indica are promising for breeding hybrid varieties with high biomass coupled with high yielding.