Two Useful Semidwarfing Genes in a Short-culm Mutant line HS90 of Rice (Oryza sativa L.).

Abstract

A short-culm mutant line HS90, which was induced from a Japanese rice variety Gimbozu by ganuna-ray irradiation, was analyzed for the genetic factors controlling its short culmness. Compared with the original variety, HS90 has about 35 o/o reduced culm length and flowers later by a few days. The F1' F2 and F3 generations of four crosses, Gimbozu X HS90, Jukkoku X Shiranui, HS90 X Jukkoku and GimbozuXJukkoku, were grown in a paddy field for genetic analysis. A variety Shiranui has already been proved to harbor a semidwarfing gene sd-1, while Jukkoku so far has been assumed to harbor sd-1 because of the cross parent of the former. In each cross, several F1 plants, about 300 F2 plants, and 50 to 90 F3 Iines which were raised from randomly selected F2 plants were examined for culm length and heading date. It was clarified that the shorten-ing of HS90 is caused by an induced mutant semidwarfing gene (tentatively sd-1h ), an incomplete recessive gene identical with or allelic to sd-1 . This mutant semidwarfing gene causes remarkable reduction of culm length (ca. 35 olo) its genotypic value in the heterozygous state seems almost equal to that of the midparent. In addition, HS90 was proved to harbor another incomplete recessive semidwarfing gene (tentatively sd(t) ) non-allelic to sd-1, which was de-rived from the original variety Gimbozu. This semidwarf-ing gene reduces culm length less than sd-1h (ca. 20 olo ) : its genotypic value in the heterozygous state seemed sorne-what larger than that of the midparent. As Gimbozu and its derivative varieties have often been used as a cross parent in Japanese rice breeding, the semidwarfing gene sd(t) seemd to be widely distributed among Japanese rice varieties. The F1 plants of HS90 (sd-1h sd-1h sd(t) sd(t) ) X Gimbozu(Sd-1 Sd-1 sd(t) sd(t) ) exhibited a culm length coming within the category of semidwarfism optimum for the present cultivation methods; hence, the genotype of the F1 plants, Sd-1 sd-1h sd(t) sd(t), was considered favorable for F1 hybrid rice varieties. In this study, it was also verified that the genotype of major-genes controlling the culm length of Jukkoku is identical with that of Shiranui, which indicates that Shiranui inherited sd-1 from Jukkoku.