Non-random distribution of the alleles for good grain filling at OsAGPS2 and OsSUT1 among a wide range of rice (Oryza sativa L.) cultivars

Rice (Oryza sativa L.) genes AS2-2 and SUT1-2, which are alleles at OsAGPS2 (AS2) on chromosome 8 and OsSUT1 (SUT1) on chromosome 3, respectively, were suggested to improve grain filling in extra-heavy panicle rice cultivars. This study examined the distribution of these alleles among 315 rice cultivars. A discriminant function based on phenol reaction of hulls, apiculus hair length and KClO3 sensitivity in seedlings was used to classify cultivars into japonica (192 cultivars) and indica (123 cultivars). Genotyping for the AS2 and SUT1 alleles were performed with In/Del and SSR markers, respectively. In japonica cultivars, the frequencies of AS2-2 and SUT1-2 were very low (3.6% and 6.3%, respectively), whereas they were more common in indica cultivars (56.1% and 74.0%, respectively). In addition, in indica cultivars the genotypes of AS2-2 SUT1-2, as well as AS2-1 SUT1-1, were more frequent than expected from independent segregation of these alleles. It was suggested that artificial and/or natural selection contributed to this non-random distribution of alleles at AS2 and SUT1. The alleles for good grain filling should, thus, be explored in indica cultivars to improve the grain filling of extra-heavy panicle types of rice in future breeding programs.