Brassica maurorum Durieu.とRaphanus sativus L.との人為合成複二倍体植物の細胞遺伝学的安定性と稔性 Cytogenetical Stability and Fertility of an Intergeneric Amphidiploid Line synthesized from Brassica maurorum Durieu. and Raphanus sativus L.

Brassica maurorum(2n = 16, FFゲノム)とダイコン(Raphanus sativus, 2n = 18, RRゲノム)との人為合成複二倍体植物Brassicaraphanus(2n = 34,FFRRゲノム)は,世代が進むとともに安定した染色体行動と高い花粉稔性を示し,比較的高い結実を示した(Table 1と3).また,Brassicaraphanusの自殖によって得られた後代植物(S_1F_1〜S_3F_1)はいずれも2n = 34の複二倍体であり(Table 2),形態的にも両親種の中間を示した(Fig.1C, DおよびE).Brassicoraphanusを種子親に育成親(B.maurorumとダイコン)を花粉親に用いた戻交雑において,Brassicaraphanus×B. maurorumの組合せは高い結実を示したが,いい結実を示したが,Brassicaraphanus×ダイコンでは不稔であった(Table 1).このうち, S_2F_1世代のBrassicaraphanus×B. maurorumの組合せから得たBC_1植物は,2n=25の染色体数をもつ二基三倍体(FFRゲノム)であった.本研究で新しく育成した複二倍体種と二基三倍体種は,MATSUZAWA et al.(1996)が提唱したI.人為合成複二倍体,II.異種遺伝子導入系統,III.異種細胞質系統IV.異種染色体添加系統およびV.染色体置換系統を育成するための橋渡し植物として利用できるものと思われた.

An intergeneric amphidiploid line, Brassicoraphanus (2n = 34, FFRR), which was synthesized from the cross of Brassica maurorum Durieu. (2n = 16, FF) × Raphanus sativus L. (cv. "4-season leaf", 2n = 18, RR), showed well-regulated chromosome behavior at the meiosis of pollen mother cells (PMCs), which resulted in higher levels of both pollen and seed fertility. All Brassicoraphanus plants obtained by selfing through three generations (S_1F_1 to S_3F_1) were true amphidiploids with the sum of the somatic chromosome number of parents being 2n = 34. They were intermediate between their parents in several morphological characteristics, such as leaf shape, inflorescence and flower characters except for white petals and the absence of root thickening. The BC_1 plants obtained from the backcrossing of the S_2F_1 plants with B. maurorum were sesquidiploid (2n = 25), exhibiting the putative chromosome number with the genomic constitution of FFR. In the present study, the amphidiploid and sesquidiploid plants produced by selfing or sib cross and backcross, respectively, from the Brassicoraphanus will be used as bridge plants for the breeding of the hybrid progenies advocated by MATSUZAWA et al. (1996).