Genetic base of Japanese soybean cultivars released during 1950 to 1988

Plant breeding success is dependent, in part, upon the genetic diversity fo und within applied breeding programs. To characterize genetic diversity in applied breeding, plant breeders have invoked the concept of genetic base, which can be defined as the ancestral pool from which breeding is derived. The genetic base of modern Japanese soybean [Glycine max (L.) Merr.] cultiv ars is not well characterized. The objective of this study was to quantify the genetic base of Japanese soybean cultivars by coefficient of parentage (CP) analysis, to compare the genetic bases of major growing regions and re lease eras in Japan, and to compare the Japanese base,vith that of other co untries. Seventy-four ancestors were identified in the pedigrees of 86 publ ic Japanese cultivars registered from 1950 to 1988, Ancestors originating f rom Japan contributed 76% of the genes to the Japanese breeding, while exot ic ancestors from the USA and Canada (US-CAN), China, and Korea contributed 2, 5, and 2%, respectively. The remaining portion of the base was of unkno wn, but presumed Japanese origin. Three major growing regions of Japan disp layed very distinct genetic bases with at least 50% of the ancestral contri bution unique to each region. Comparisons revealed that the Japanese base w as more diverse than that of the US-CAN. The more diverse genetic base was exemplified by (i) more ancestors accounting for 50 and 80% of the genes in Japanese breeding; (ii) a continual expansion of the genetic base since 19 50, while the US-CAN base remained relatively static; and (iii) a higher ra tio of ancestors employed;to cultivars released. The number of ancestors co ntributing to breeding-in Japan was much smaller than that for China in ter ms of number of ancestors, even though both genetic bases expanded with tim e. The long history of soybean breeding in Japan, its diverse genetic base and its relative isolation from US-CAN and China suggest that Japanese, Chi nese, and North American breeding pools may serve as important reservoirs o f diversity for each other. Twelve Japanese cultivars released from 1950 th rough 1988 derived at least 25% of their pedigree from improved U.S. or Chi nese breeding materials.