QTL-based analysis of heterosis for grain shape traits and seedling characteristics in an indica-japonica hybrid in rice (Oryza sativa L.)

A set of BC1F1, i.e., indica/japonical/japonica and indica/japonical/indica, were produced to specifically compare the effect of heterozygotes and homozygotes at each QTL locus in an indica-japonica hybrid in rice. Grain shape traits and seedling characteristics were measured, in BC1F1 and BC1F2, respectively. Five QTLs were detected for grain width on chromosome 1, 2, 5 and 7. Two QTLs were detected for the 1000-grain weight on chromosomes 4 and 5. Three QTLs were detected for the grain thickness on chromosomes 2 and 5. Four QTLs were detected for the seedling weight on chromosomes 5, 6 and 12, in addition to three QTLs for other seedling traits, length of first leaf, seedling height and chlorophyll content, on chromosomes 1, 3 and 6, respectively. In the comparison of marker genotypes of AA, Aa and aa, QTLs were detected either between AA and Aa or between Aa and aa, and there was no case in which Aa was superior to AA and aa. In both analyses, each positive effect was contributed from either one of the parents. So far as the present data concern, it was able to conclude that the high level of heterosis in the current indica-japonica hybrids was manifested by a cumulative partial dominant effect of the heterozygotes at many loci and not by over-dominance. Then, the set of QTL data for positive effects are considered to be systematically utilized in breeding of parental lines by using molecular markers.