Transmission of kale chromosomes from the monosomic addition lines (2n = 19) to four radish cultivars (2n = 18)

本研究では,交雑親和性の低いダイコン品種にカンラン類の一染色体を添加するため,a～g添加型ダイコンと日木の主要ダイコン4品種との交雑を行なった.その結果,いずれの添加型ダイコン×ダイコン4品種の正逆交雑においても花粉発芽指数は高かった.添加型ダイコン×ダイコン4品種では,受精前後の結果がよかったことから,受精-胚発育が早いことを示唆した.また,受粉後17日頃までは2n = 19の染色体数を持つ胚もかなり生存していたものと考えられた.しかし,胚発育の中・後期に至り,胚の退化も考えられた.一方,ダイコン4品種×添加型ダイコンの場合は,花粉間競争によってn=10を持つ配偶子は遅延したり,一部は受精後の早期に死滅した可能性がある.しかし,比較的種子稔性が高かったことから,受粉17日以降もかなりの胚が生育したものと思われる.F_1植物における7種類の添加染色体の伝達率は,添加型ダイコン×ダイコン4品種では5.9 %,逆交雑では1.1%であり,いずれの組合わせからも添加型ダイコン(2n = 19)が得られた.さらに,4種類の添加型B_1 F_1植物(a, e, fおよびg添加型, 2n = 19)×ダイコン4品種における伝達率でもダイコン4品種間で大きな差異がみられなかった.以上のことから,既成の添加型ダイコンを橋渡し植物としてダイコン4品種の遺伝的backgroundを持ったカンラン類一染色体添加型ダイコン(2n=19)の育成ができるものと結論できた.We have bred seven types of monosomic alien chromosome addition lines of radish (a～g types of cv. Shogoin with the kale chromosome, 2n = 19) with the offspring of Raphanobrassica, which were backcrossed with cv. Shogoin (2n = 18). In this study, to ensure the transmission of the kale chromosome, hybridization was performed between the above chromosome addition lines and four leading cultivars of radish. Pollen germination was successful in the reciprocal crossings when evaluated by the levels of pollen germination index. In the crossing of monosomic addition lines × four radish cultivars, the rates of ovule with pollen tube penetration, the developed ovules and well-grown embryos made a good score at 17 days after pollination. These rates suggest a more favorable reproduction process from the zygotic to the middle embryonic stages, although embryo degeneration was recognizable to some extent at the end of embryo growth. In the reciprocal crossing, however, it was estimated that male gametes having n = 10 were handicaped in the competition with the gametes (pollen) of n = 9 or most of the embryos of 2n = 19 might degenerate at an early stage in the fertilization process. As a result, fertile seeds of radish with kale single chromosome were harvested in this crossing. The transmission rates of the seven types of monosomic alien chromosome addition lines with the added kake chromosome were 5.9 % for the F_1 generation of the crossing of (a～g) types × four radish cultivars and 1.1% for the reciprocal crossing. In the cross of four types of kale monosomic addition lines (B_1F_1, a, e, f and g types) × four radish cultivars, the transmission rates were scarcely fluctuated by four radish cultivars. The kale monosomic addition lines with the genetic background of four radish cultivars were successfully developed and provided some materials for the genetical research in the potential traits in radish breeding