Abstract
It is a well known fact that the hybrid sterility is not found frequently in rice when Japonica type varieties are crossed with Indica type ones.. On the other hand, it is also known that the sterility occurs in tetraploid plants when diploids are artificially doubled in chromosomes. In the previous paper. MASIMA reported with UCHlYAMADA about some relationships between the two types of sterility and concluded that the fertility of subspecific hybrids, showing high sterility in diploid level is recovered in some degree when they are doubled to the tetraploid level (MASIMA and UCHIYAMADA 1955). This reason was considered due to the selective pairing among the four homologous chromosomes which have small structural differences between the two original varieties. Here another brief report is given as we recognize.d the same conclusions by a successive experiment using new materials. Tetraploids were newly induced in 38 Iines using 11. other varieties. They are grouped in to four different kinds of tetraploids, originated from simple varieties, fertile varietal hybrids (intra-subspecific hybrids), semisterile ' varietal hybrids (inter-subspecific hybrids) and sterile varietal hybrids (inter-subspecfic hybrids) .
