Varietal Difference in Yield Structure of Wheat

Abstract

The differences in source/sink balance and yield formation among 33 Japanese and 17 foreign wheat cultivars bred in different eras were evaluated using individual kernel weight, the number of kernels m^-2 and total dry matter at heading and maturity in a field experiment. The mean individual kernel weight (KW) at maturity of the spike from which two-thirds of spikelets were removed at the heading stage was assumed as an index of the potential maxim kernel weight (PKW). The source/sink balance of cultivars were evaluated by the ratio of KW/PKW which represents the ratio of kernel filling by its sink strength to PKW. The products of total number of kernel (N) and KW were assumed as the yield. The yield formation was evaluated by the increase in total dry matter from heading to maturity (amount of dry matter produced at ripening stage) and the contribution of the dry matter accumulated before heading among the yield. The mean KW/PKW of the domestic cultivars bred after 1980s was higher (0.783) than those bred before 1980s (0.730). Some of the foreign cultivars also had higher KW/PKW (0.751–0.810). The ratio of dry matter accumulated before heading to the yield exceeded 30% in 9 of 21 cultivars bred before 1980s. Some foreign cultivars showed negative KW/PKW, which implied that yield formation depended only on the amount of dry matter produced at the ripening stage. The cultivars used in this study were classified into two groups with KW/PKW higher than 0.741 (I) and lower than 0.741 (II), and also into these groups with a ratio of dry matter accumulated before heading to yield higher than 21.2% (A), 0% to 21.2% (B) and less than 0 % (C).