Gene Analysis for the Semidwarfism of Two Mutant Strains, Hokuriku 100 and Kanto 79, Induced from a Rice Variety Koshihikari : Studies on the Utility of Artificial Mutations in Plant Breeding XVIII

Abstract

Two semidwarf mutant breeding lines, Hokuriku 100 and Kanto 79, which were induced from a Japanese rice variety Koshihikari by gamma-ray irradiation, were analyzed for their semidwarfing genes. Compared with the original variety, Hokuriku 100 and Kanto 79 have 30 and 40% reduced culm length, respectively, and the latter flowers earlier by 10 days. The F₁, F₂ and F₃ generations of three crosses, Koshihikari×Hokuriku 100, Koshihikari×Kanto 79 and Hokuriku 100×Kanto 79, were grown for genetic analysis. In each cross combination, several F₁ plants, 223 to 334 F₂ plants and 100 F₃ lines which were raised from randomly selected F₂ plants were examined for culm length, heading date and seed fertility. It was clarified that the semidwarfism of Hokuriku 100 is controlled by one recessive semidwarfing gene (tentatively sd(t)) which was induced in Koshihikari, and this semidwarfing gene could not manifest itself until a gametic-lethal gene of Koshihikari (tentatively lt), which is inherited independent of sd(t), mutated to its non-gametic-lethal allele (tentatively lt^m). The semidwarfism of Kanto 79 proved to be due to the pleiotropy of one recessive early-heading gene (tentatively eh^e) which was induced in Koshihikari. This gene was nonallelic to and independent of the above two genes sd(t) and lt, and had no interaction with the gametic-lethal gene lt. These experimental results suggest that in the cross breeding to introduce the semidwarfing gene of Hokuriku 100 into some varieties or strains, a much larger number of offsprings are needed than in usual, and that the breeding aiming at early maturity as well as semidwarfism, Kanto 79 can be adopted as an excellent cross parent. The facts that the semidwarfing gene detected in Hokuriku 100, sd(t), did not influence any agronomic characters other than culm traits and did show a unique interaction with a garnetic-1ethal gene, and the evidences that sd(t) is non-allelic to d-47 as well as to sd-1 and d-49(t), indicate that sd(t) is the gene different from all the semidwarfing and dwarfing genes so far reported. So, the authors have designated this newly detected semidwarfing gene as d-60.