Classification of male sterile cytoplasms and fertility restoring genes in rice : 1. Identification of male sterile cytoplasm and fertility restoring gene of RT61 line for BT line

野生稲由来のRT61系統(総称)および栽培稲由来のBT系統(総称)はいずれも台中65号の同質遺伝子系統であり, ともに雄性不稔細胞質(cms)と一対の稔性回復遺伝子(Rf-rf)との相互作用によって雄性不稔性またはその稔性回復性を示し, 花粉稔性は配偶体支配である.両系統の細胞質および稔性回復遺伝子の異同を調べるためにそれぞれの細胞質雄性不稔系統(RT61AおよびBTA, 遺伝子型(cms)rfrf)および稔性回復系統(RT61CおよびBTC, 遺伝子型(cms)RfRf)と台中65号(n)rfrfを用いて交雑実験を行った.RT61A/BTCおよびBTA/RT61CのF_1はいずれも全個体が花粉半稔・種子正常稔となり, 両系統に細胞質差はみられなかった.RT61C/BTCおよびBTC/RT61CのF_1稔性はともに全個体が花粉完稔・種子高稔となった.したがって, ここでも細胞質差は見られず, また不稔花粉が生じてないことから, 両系統のもつ稔性回復遺伝子は同座かもしくは強い連鎖であると考えられた.RT61A/BTCおよびBTA/RT61Cの両F_1に台中65号を花粉親として交雑すると, 母本となったF_1の交雑方向に関係なく花粉半稔・種子高稔個体と花粉完全不稔・種子完全不稔個体が1 : 1に分離した.このことは, それぞれの稔性回復遺伝子が相手細胞質のもとで正常に働いて胚のうを通して正しく伝達されていることを示している.RT61C/BTCおよび BTC/RT61CのF_1に台中65号を花粉親として交雑した三系交雑F_1はいずれの場合も, 全個体が花粉半稔・種子高稔個体となり, 不稔個体を生じなかった.これは両系統の稔性回復遺伝子が同座である場合の分離に適合していた.以上の結果から, 両系統の細胞質は同一タイプであり, また稔性回復遺伝子は同一作用を示す同座の遺伝子であると結論づけられた.RT61 line (derived from Oryza rufipogon) and BT line (derived from O. sativa) which are isogenic lines of Taichung 65 indicated similar inheritance of male sterility. In order to determine whether the cytoplasms and fertility restoring genes of these two lines are identical, the following crossing experiments were carried out. In the cross of the male sterile line/restorer all the F_1 progenies produced fertile pollen in half of the cases while seed fertility was normal regardless of the kind of paternal (or maternal) lines. In the reciprocal crosses of restorer/restorer since all the F_1 plants produced complete fertile pollen and seeds with fertility, there was no difference in the cytoplasms and the fertiliy restoring genes between the two lines. However, since it was difficult to determine whether the restoring genes were present at the same locus or were closely linked, three-way croses were conducted. First, F_1s of the male sterile line/restorer were crossed with Taichung 65. In the offsprings there were plants with complete sterile pollen and sterile seeds and plants with fertile pollen in half of the cases and fertile seeds in a ratio of 1 to 1. It was therefore confirmed that the fertility resoring genes were transmitted normally in other cytoplasms. Thereafter the F_1s of restorer/restorer were pollinated with Taichung 65. Assuming that the fertility restoring genes of these lines were linked and present at a different locus, segregation of male sterile plants would be expected. However, the results indicated that all the F_1 progenies formed normal pollen and seeds. Therefore, the fertility restoring genes of these lines were considered to display the same function for fertility and to be at the same locus. The above results sugested that the male sterile cytoplasms of the RT line and BT line belonged to the same type for fertility restoration, and the nuclear fertility restoring genes were present at the same locus with the same function