Studies on Varietal Differences in Vernalization Requirement in Wheat

Besides spring and winter wheats, various kinds of intermediate wheat are cultivated in Japan. KAKIZAKI and SUZUKI (1937) classified Japanese wheats into 7 grades according to their heading behavior upon successive sowing in spring. Grade I corresponds to the extreme spring habit of growth, and grade VII to the extreme winter habit. The classification has been found adequate for the explanation of the ecological distribution of wheat in Japan. Although the fundamental idea of the classification lies in an evaluation of the degree of vernalization requirement, some inconsistency may take place between the grades of growth habit estimated by successive sowing and the vernalization requirement on account of day length effect on heading time.