Gene Analysis of the Degree of Vernalization Requirement in Winter Wheat

Through genetic studies of the vernalization requirements of winter wheats, it was made clear that the varietal differences of vernalization requirements in winter wheat are gener-ally controlled by alleles of major genes which have mainly an additive effect. Two such genes were discovered to be involved in the expression of the varietal differences of the vernalization requirements of winter wheat. The gene tentatively named Aa is responsiblp for the difference in the vernalization requirements between cultivars with 20 days' requi-rement and cultivars with 40 days' requirement. A Iow level of vernalization requirement is incompletely dominant over a high level of requirement. The Bb gene is responsible for the difference between a vernalization requirement of 40 days and that of 60 days, where a low level of requirement is dominant over a high level of requirement, although the domi-nance effect is weaker than the former case. Because of the experimental procedure, the allelic relation between Aa andBb is unknown at present. In addition, the allelic relation of these alleles to the Vrn genes is a matter of future investigation. Besides major genes, minor genes were found to be responsible for the varietal differences in ver-nalization requirement. Namely, the difference between Akasabi Shirazu 1, which has a vernalization requirement of 60 days, and cultivars with a vernalization requirement of 40 days was found to be attributable to the curnulative effect of minor genes.