Partial dominance in Actinidia kolomikta interspecific hybrids

Actinidia kolomikta is primarily a diploid species that is crossable in two directions thereby providing an efficient means for interspecific gene transfer. A. kolomikta has several desirable attributes such as cold hardiness, compact growth habit, precocity, and a short growing season to achieve fruit maturity. In Minnesota, A. kolomikta has been crossed with seven other Actinidia species to produce various interspecific hybrids that exhibit mostly intermediate vegetative, phenologic and physiologic characteristics. A comparison of progeny from four corresponding reciprocal crosses suggests that partial dominance is the prevailing, but not exclusive form of inheritance. Depending on the cross, seedling hybrids may display various degrees of genetic incongruity including stunting, chlorosis and albinism, but the residual population tends toward more vigorous initial growth than that for A. kolomikta control seedlings; and in A. kolomikta × A. chinensis a predominance of male plants rather than equal proportions of sexes has been identified. This suggests the possibility of sex-controlled linkages. The reciprocal hybrids and many of the A. kolomikta seed parent interspecific hybrids lack sufficient cold hardiness to survive Minnesota's harsh winters necessitating potted culture for some crosses. The seed parent imparts a prevailing, but not complete, influence on cold hardiness as progeny from these wide crosses typically have an intermediate tolerance to freeze injury. Phenologically, the timing of bud break, leaf burst, flowering and leaf senescence in the hybrids differ from the A. kolomikta parent. In potted culture, chlorosis and albinism are most pronounced in the spring following the emergence of new vegetative growth when soil and nightly air temperatures rcool. Leaves green up with the advent of warmer conditions. Hybrid leaves differ in form from either parents, but display a closer affiliation with the seed parent with respect to shape, color, serration, venation patterns, surface texture and extent of pubescence.