Phylogenetic differentiation of the cultivated rice. XVII. Sterility and vigor of lines derived frorn hybrids between distant varieties of rice in crosses with parental varieties.

F7 or F8 Iines taken at random from populations of hybrids between distant varieties (the same materials as reported in the 16-th contribution of, this series) were crossed with the parental varieties or a certain variety ' chosen as tester, and the variation among those lines in reaction-type of hybrid sterility was investigated. Various reaction-types were found, and it vJas pointed out that most of lines had reaction-types like one or the other parent, and that lines producing fertile hybrids with one parent tended to produce semi-sterile hybrids with the other. This may imply tb.at a number of sets of "GameticDevelopment genes" are present in the parental varieties, and they are linked with one anotber. Lines similar to one parent in the reaction-type of hybrid sterility tended to have characteristics similar to those of parent. This may be due to the linkage of "G.D. genes" with genes responsible for those chal acters. It was found furth ?? r that lines similar to one parent in the reaction-type of hybrid sterility or in the tender.Lcy of character combination tend to show a hybrid vigor in crosses with the other parerLt. It was discussed that the restriction of recombinations due to the "G. D. genes" might work as an isolating mechanism between distantly related varieties of rice.