Abstract
The objectives of this study were to evaluate the main effects and interactions of individual quantitative trait loci (QTLs) for grain length and their combinations in rice. Five primary near-isogenic lines (NILs), each of which had an allele for long grain only at one of five QTLs controlling grain length of a large-grain cultivar, 'BG 1', and an allele for short grain length at the other four QTLs, were constructed with a common genetic background of a small-grain cultivar, 'Gimbozu'. In addition, an NIL involving a major gene for long grain of 'Fusayoshi', Lkf, in the same background as above was developed. From intercrossing of these primary NILs, phenotypic selection, and progeny tests, 15 advanced NILs, each of which had different alleles for long grain only at one of the 10 combinations of five QTLs, and one of the five combinations of five QTLs and Lkf, were further constructed. The main effects (additive effects) and interactions (epistatic interactions) of QTLs and Lkf on grain length were estimated from the mean grain lengths of these NILs and 'Gimbozu' cultivated over two years. The main effect of Lkf was the largest, followed by those the QTLs showing a large and significant variation among them. The correlation coefficient between the two years for the main effects was high and significant (r=0.95*), suggesting that the QTLs' main effects were consistently expressed at their own magnitudes for the two different years. The interactions between two QTLs were about half the strength of the main effects in their magnitudes and also showed a large, significant variation among QTLs. The year-to-year correlation for the interactions was, however, not significant (r=0.63). These results suggested that QTL-by-QTL interactions could contribute to the instability of character expression and could play an important role in genetic systems controlling quantitative traits.
