A Study on Cross Breeding between Triploid and Diploid Apple Cultivars

在苹果杂交育种中，三倍体品种(3x)迄今很少被用作育种材料。也就是说，在二倍体品种(2x)之间进行杂交是一种惯例。在这种情况下，本研究旨在建立三倍体和二倍体苹果品种间的杂交育种方法。以三倍体和二倍体品种正反交为试材，对其树体生长、开花结果、果实性状等进行了比较研究。在幼树生长方面，2x×3x组合的苗木生长优于3x×2x苗木。在2x*3x苗木中，生长势与2x*2x苗木相当的占39%~54%。相当多的2x×3x苗木表现矮化。将2x*3x苗木嫁接到苹果生根上，以树干周长为指标，约有50%的苗木表现矮化。因此，可以清楚地认识到，2x×3x的矮化杂交苗嫁接到有活力的砧木上时也表现出矮化。在开花结实方面，2x*3x杂交苗次于2x*2x苗，但明显优于3x*2x苗。播种7年后，2x×3x苗与2x×2x苗的果实性状差异不明显，但因杂交组合的不同而表现出差异。结果表明，以二倍体品种为种子亲本，以三倍体品种为花粉亲本进行杂交育种效果较好，育成矮秆品种的可能性较大。

In cross breeding of apple, triploid cultivars (3x) have been scarcely employed hitherto as the breeding materials. Namely, it has been a practice to perform intercrosses among diploid cultivars (2x). Under these circumstances, this study aims at establishing a method of cross breeding between triploid and diploid apple cultivars. Thus, seedlings were grown from reciprocal crosses between triploid and diploid cultivars and comparison was made on the tree growth, flowering, bearing, fruit characteristics, etc.1. Regarding the growth of young trees, seedlings of 2x * 3x crosses were superior to 3x * 2x seedlings. Among the 2x * 3x seedlings, those showing vigorous growth comparable to 2x * 2x seedlings amounted to 39 to 54%. A considerably large number of the 2x * 3x seedlings showed dwarfness.2. When the 2x * 3x seedlings were grafted on vigorating rootstocks, Malus prunifolia, about 50% of the seedlings showed dwarfness evaluated on the basis of trunk circumference index. Thus, it was clearly recognized that dwarf cross seedlings of 2x * 3x also showed when grafted onto vigorating rootstocks.3. In flowering and fruiting, the cross seedlings of 2x * 3x were inferior to the 2x * 2x seedlings but clearly superior to the 3x * 2x ones.4. Seven years after sowing, the cross seedlings showed difference in fruit characteristics depending on cross combination, though no clear difference was observed between the 2x * 3x seedlings and the 2x * 2x ones. However, these seedlings have just attained the bearing age and therefore the investigation should be continued further.These results indicate that cross breeding can be well performed by using a diploid cultivar as the seed parent and a triploid cultivar as the pollen parent, and that there is a high possibility of creating a dwarf cultivar.