EPISTASIS PLAYS AN IMPORTANT ROLE AS GENETIC-BASIS OF HETEROSIS IN RICE

The genetic basis of heterosis in rice was studied in a cross between Zhenshan 97 and Minghui 63, the parents of the best hybrid widely used in rice production in China. Field data for yield and yield component s traits were collected over two years from 240 F-2:3 families of this cross planted in replicated field trials. These families were assayed with 151 marker loci that were polymorphic between the parents and a linkage map was constructed with Map-maker analysis. A total of 32 qua ntitative trait loci (QTLs) were identified for yield and the three co mponent traits; 12 QTLs were detected in both years and the remaining 20 QTLs were observed in only one year. A search for the entire genome by using two-way analyses of variance with all possible two-locus com binations detected a very large number of significant digenic interact ions involving both the QTLs resolved by single-locus analysis and loc i that did not show significant effects by single-locus analysis. Many of the interactions were simultaneously detected in both years. Parti tioning of the epistatic interactions recovered all three types of int eractions, i. e. additive by additive, additive by dominance and domin ance by dominance, for all the traits. Some of the epistatic interacti ons even showed pleiotropic effects by simultaneously affecting two or more traits. The results clearly indicate that epistasis plays a sign ificant role in the inheritance of yield traits as well as in the gene tic basis of heterosis.