Quantitative trait loci controlling the number of spikelets and component traits in rice: Their main effects and interaction with years

To develop superior rice panicles with a sufficient sink capacity and a high degree of grain filling, we should consider the within-panicle distribution of spikelets showing different degrees of grain filling, as well as the total spikelet number. In the present study, several component traits of the number of spikelets per panicle which are related to the within-panicle distribution, and also the number of panicles per plant, were examined using 68 recombinant inbred lines (RILs) derived from a cross of Asominori/IR24 grown over a period of four years, 1997, 1998, 2000 and 2001. For every trait related to the spikelet number per plant, analyses of variance (ANOVA) were conducted at the 375 position of molecular markers one by one to detect significant main effects of quantitative trait loci (QTLs) and interactions of marker genotype and year of cultivation (QY interactions). Then, genetic associations of these traits were analyzed by examining the positions of the relevant genome regions which showed significant main effects and/or interactions for different traits. Finally, the QTLs causing favorable genetic effects and associations for the development of superior panicles were surveyed. The results showed that most of the genome region identified to increase the spikelet number per panicle also increased the number of spikelets on the secondary branches which are characterized by a low degree of grain filling. One region on chromosome 3, on the other band, increased the spikelet number per panicle through the increase of the number of spikelets on primary branches which generally show a high degree of grain filling. Significant QY interactions were demonstrated in many genome regions for all traits, whereas the interactions of RIL and year could not be detected in an overall ANOVA in which the marker genotypes of RILs were not being considered. The region on chromosome 3, cited above, did not exhibit a significant QY interaction. This region appears to involve QTL(s) suitable for the development of superior panicle types.