リンゴ二倍性品種と三倍性品種の正逆交雑における初期生育の良好な実生の獲得効率の比較と育種の可能性(育種・遺伝資源)  [in Japanese] Comparison of the EWstablishment Efficiency of Well-grown Seedlings at the Early Growth Stage from Reciprocal Crosses between Diploid and Triploid Apple Cultivars, and the Possibility of These Cultivars Cross Breeding(Breeding & Germplasm Resources)  [in Japanese]

リンゴ二倍性品種(2x)と三倍性品種(3x)の交雑育種の可能性を探るため,二倍性品種の発育良好な中心花に三倍性品種の花粉を多く受粉して2x×3xの交雑組合せを設けた.その2x×3xと3x×2x,2x×2xの組合せで2回の摘果を実施した後,着果と種子形成,実生の初期生育などを調べ,交雑した100花当たりで得られる生育良好な実生の数を比較検討した.受粉後60日の着果率は3x×2xがフロ〜81.6%,2x×2xが92.9〜98.0%に対し,2x×3xは16.5〜36.5%であった.完全種子の形成率は2x×2xが76.5〜77.5%に対し,2x×3xと3x×2xは9.4〜42.6%と著しく低く,後二者の交雑組合せの間で差違は認められなかった.播種後1年の樹齢で生育良好な実生割合は2x×3xが47.3〜54.0%,3x×2xが2.4〜7.2%,2x×2xが72.4〜94.1%であった.これらのことから,100交雑花当たりで得られる初期生育の良好な実生数を算出した.その結果,実生数は2x×3xか24〜93本,3x×2xが1〜13本,2x×2xが456〜772本であった.すなわち,受粉と摘果の方法を工夫することにより,2x×3xでは3x×2xより初期生育の良好な実生を多く獲得できることが分かった.この実生の獲得効率の比較から,2x×3xは2x×2xに比較して育種の効率は劣るものの,新品種育成の可能性があると考えられる.一方,3x×2xではその可能性は小さいと推察される.

This study investigated the possibility of performing cross breeding between diploid (2x) and triploid (3x) apple cultivars. Well-grown king flowers of 2x were hand-pollinated with an abundance of pollen grains from the 3x; thinning for open-pollinated fruitlets on the experimental trees was carried out twice for the 2x × 3x, 3x × 2x and 2x × 2x crosses. Thereafter, the three types of crosses were compared for fruit set, seed formation, seedling growth at the early growth stage, and the number of well-grown seedlings established from 100 flowers crossed. Fruit set 60 days after pollination was 71.1 to 81.6% and 92.9 to 98.0% for 3x × 2x and 2x × 2x, respectively. For 2x × 3x, however, fruit set ranged from only 16.5 to 36.5%. Rate of normal seed formation was 76.5 to 77.5% for 2x × 2x, but only 16.5 to 42.6% for 2x × 3x and 9.4 to 33.6% for 3x × 2x. Rate of well-grown seedlings 1 year after sowing ranged from 47.3 to 54.0% and 2.4 to 7.2% for 2x × 3x and 3x × 2x, respectively, and 72.4 to 94.1% for 2x × 2x. Number of well-grown seedlings established from 100 flowers crossed was 456 to 772 for 2x × 2x, 24 to 93 for 2x × 3x and 1 to 13 for 3x × 2x; it was found that more well-grown seedlings can be obtained for 2x × 3x than for 3x × 2x, using the techniques of pollinating and fruit thinning described above. These findings show that cross breeding for a new apple cultivar will be successful for 2x × 3x, though the cross is less efficient for breeding than the 2x × 2x. Breeding from a 3x × 2x cross will have little success.