Abstract
Forty-three soybean cultivars released from 1915 to 2001 in the western region of Japan were divided into three groups, I, II and III, by the released year and evaluated for their characteristics. Old cultivars included in groups I and II had great diversities in some characteristics, but new cultivars included in group III had decreased diversity. Flower color and pubescence color were unified to purple and grey, respectively in group III. Groups I and II contained nearly the same number of early, medium and late maturing cultivars, but almost all cultivars showed medium maturity in groupIII, because cultivars with intermediate maturing type were widespread in this period. The seed-filling period of cultivars in group III was longer compared with that in groups I and II, which was considered to be advantageous for high yield. Plant height and the number of nodes were decreased in group III, which contributed to the improvement of lodging resistance significantly. However, the yield advantage was not found in the cultivars of group III compared with the cultivars of groups I and II. The decrease in the number of nodes was associated with the decrease in pod number, so the seed yield of the new cultivars was not increased though 100-seed weight increased. Although the new cultivars, ‘Tamahomare’ and ‘Sachiyutaka’ had shorter stems and fewer nodes than cultivars of groups I and II, they had a seed yield as high as that of high-yielding late maturing cultivars. The seed quality such as protein content was consistently improved in newly released cultivars.
