IMPORTANCE OF EPISTASIS AS THE GENETIC-BASIS OF HETEROSIS IN AN ELITERICE HYBRID

The genetic basis of heterosis was investigated in an elite rice hybri d by using a molecular linkage map with 150 segregating loci covering the entire rice genome, Data for yield and three traits that were comp onents of yield were collected over 2 Sears from replicated field tria ls of 250 F-2:3 families, Genotypic variations explained from about 50 % to more than 80% of the total variation, Interactions between genoty pes and gears were small compared with the main effects, A total of 32 quantitative trait loci (QTLs) were detected for the four traits; 12 mere observed ill both years and the remaining 20 were detected in onl y one year, Overdominance was observed for most: of the QTLs for yield and also for a few QTLs for the component traits, Correlations betwee n marker heterozygosity and trait expression were low, indicating that the overall heterozygosity made little contribution to heterosis, Dig enic interactions, including additive by additive, additive by dominan ce, and dominance by dominance, were frequent and widespread in this p opulation, The interactions involved large numbers of marker loci, mos t of which individually were not detectable on single-locus basis; man y interactions among loci were detected in both years, The results pro vide strong evidence that epistasis plays a major role as the genetic basis of heterosis.