Allelic interaction causing gamete abortion in wide crosses of cultivated rice was earber identified at locus S-5 on Chromosome 6 and recently at locus S.7 on Chromosome 7 At S-5 1ocus Indica and Japonica does have S-5i and S-5j, respectively, and Javaaicas such Ketan Nangka have a neutral allele 3-5n. The S-5i/S-5j genotype produces semi-sterile panieles due to abortion of female gametes carting S-5j, but both S-5n/S-5i and S-5n/S-5j genotypes do not. The S-5n is called "wide compatibility gene" (WCG), as one of parents possessing this allele does not show hybrid sterility in their F1. The WCG has been used for breeding hybrid varieties between Indica and Japonica rice. The S-5n allele was incorporated from Ketan Nangka to Japonica lines such as Nekken 1 or 2, which do not show semi-sterility in their cross to many Indica type. However, Nekken 2 showed typical hybrid sterility when it was crossed to a Korean Indica line. Yeong Pung. Therefore. a new Iocus was suggested for the semi-sterility in that hybrid. By genetic analyses using isozyme markers, a new locus for the hybrid stenhty between Nekken 2 and the Korean Indicas was located near Cat-I locius on Chromosome 6, and designated as following our recent report on S-7 On the basis of allelic interaction causing fenale gamete abortion, three alleles were found at S-8 follows: a Japonica line Nekken 2 and Yeong Puny possess S-8kn and S-8yp, respectively, and their hybrid genotype of S-8kn/S-8yp shows semi-sterility a portion of female gametes carrying S-8kn was aborted A Japonica tester variety, Akihikari was found to have a neutral allele, S-8n at this locus, and another neutral allele, S-7n at S-7, A possibility to cumulate three neutral alleles in a breeding line is suggested to solve hybrid sterility problem in wide crosses of rice.