Distribution of fertility-restoring genes in commercial lowland-rice varieties cultivated in Japan for two male sterile cytoplasms of rice (Agricultural Experiment Station)

Lead Rice細胞質をもつ完全雄性不稔系統(cms-2)およびOryza perennisの1系統の細胞質をもつ完全雄性不稔系統(cms-3)に対する稔性回復遺伝子の有無を明らかにするため, cms-2×213日本水稲奨励品種, cms-3×214日本水稲奨励品種の交雑を行なった。各交雑組合せとも5個体のF_1を栽植し, 花粉稔性と種子稔性を調べ, 父本品種が稔性回復遺伝子をもつかどうかを決定した。1.cms-2に対する213品種のうち, 27は稔性回復遺伝子を, 186は非稔性回復遺伝子をもっていた。稔性回復遺伝子をもつ27品種のうち22は京都以南に, 5は京都以北に分布し, 逆に非稔性回復遺伝子をもつ品種は京都以北で分布頻度が高く, 京都以南においては低い。すなわち該遺伝子の分布に地理的傾斜がみられる。稔性回復遺伝子をもつ27品種のうち, 19(70.4%)は在来品種から純系分離育種法で, 残り8(29.6%)は交雑育種法で育成されたものであった。2.cms-3に対しては214品種のすべてが非稔性回復遺伝子をもっていた。このことは日本稲でcms-3細胞質をもつ雄性不稔系統の育成がきわめて容易であることを示している。cms-3細胞質に対する効果的な稔性回復遺伝子が発見されるならば, cms-3細胞質とその回復遺伝子は日本における雑種稲育種の基礎研究に広く活用されるであろう。3.cms-2とcms-3に共通に作用する稔性回復遺伝子系統はひとつも発見されなかった。したがって両細胞質は異質のものと考えられる。In order to investigate the presence of a fertility-restoring gene or genes for a completely male-sterile strain with Oryza sativa cv. Lead Rice cytoplasm (cms-2) and a completely male-sterile strain carrying the cytoplasm of O. perennis, 213 commercial lowland-rice varieties of Japan were crossed to the former strain and 214 varieties to the latter. From the F_1 progeny of each cross, five plants were planted to examine their pollen and seed fertilities and also to determine whether to be varieties having fertility-restoring gene(s) or not. For cms-2 strain, 27 of the 213 varieties possessed fertility-restoring gene(s) and the remaining 186 carried non-restorers. Out of the 27 varieties carrying fertility restorers, 22 were distributed in the southern region of Japan (Kyushu, Chugoku, Shikoku and Kinki districts) and the remaining five were present in the northern region (Chubu, Kanto, Tohoku, and hokkaido districts). On the other hand, out of 186 non-restorers, 111 were distributed in the northern and 75,in the southern region. The frequency of the gene(s) was higher in the northern than in the southern region. Of the 27 varieties having restorers, 19 (ca. 70%) were bred by pure-line selection from their naive ones and the remaining eight (ca. 30%) were by the hybridization breeding methods. For cms-3 strain, all of the 214 varieties possessed non-restoring genes. It suggests that male-sterile lines of japonica with the cytoplasm of cms-3 can be bred easily. If an effective restorer for cms-3 cytoplasm is discovered, the cytoplasm and its fertility-restoring gene(s) will be utilized extensively in the basic studies on hybrid rice breeding in Japan. In the present investigation, the fertility-restoring gene9s) for cms-2 cytoplasm did not restored fertility in the cms-3 cytoplasm. It indicated that the above two cytoplasms were of different nature in each other