Characteristics of Dry Matter Production in Sachiyutaka, a New Soybean Cultivar in Southwestern Japan

The purpose of this study was to determime the characteristics of dry matter production in Sachiyutaka, a new soybean cultivar in southwestern Japan in comparison with Fukuyutaka, a conventional cultivar in the region. Soybean plants were grown in the field in 2001 and 2002. The flowering time and the maturation time were earlier and vegetative growth was poorer in Sachiyutaka than in Fukuyutaka, but the ratio of grain to stem was clearly higher in Sachiyutaka, and there were no significant differences in seed yield between the two cultivars. Growth parameters such as leaf area index (LAI), crop growth rate (CGR), total dry matter and stem dry weight were slightly higher in Sachiyutaka until flowering, but the increase in those parameters after flowering were more rapid in Fukuyutaka. No differences in photosynthetic rate, net assimilation rate (NAR) or pod growth rate were observed between the two cultivars, though the beginning of pod growth was earlier in Sachiyutaka. The stem dry weight and the concentration of total nonstructural carbohydrate in the stem decreased after flowering in both cultivars, but the degree of the decline was larger in Sachiyutaka than in Fukuyutaka. Those results suggested that the carbohydrate stored in the stem was translocated to developing fruit more in Sachiyutaka than in Fukuyutaka. In conclusion, high seed yield in spite of low total dry weight in Sachiyutaka is caused by the early completion of vegetative growth and the retranslocation of stored nonstructural carbohydrate from stems to fruits during pod filling period.