Phenotypic Diversity of Modern Chinese and North American Soybean Cultivars

Abstract

Chinese and North American (NA) soybean breeding programs have a 70‐yr history of genetic progress in relative isolation from each other. Because both programs rest upon a genetic base that is primarily Chinese in origin, the actual genetic distinctness of Chinese and NA breeding is not clear. The objectives of this study were to (i) develop a phenotypic similarity (PS) index for a large group of Chinese and NA cultivars, on the basis of biochemical, morphological, and agronomic traits, (ii) compare Chinese and NA cultivars for PS through cluster analysis, and (iii) use results to develop guidelines for management of the contrasting Chinese and NA breeding programs as reservoirs of diversity. Chinese (47) and NA (25) cultivars were evaluated for 25 traits in growth chambers. Traits pleiotropic to maturity were avoided. Significant (P < 0.05) differences between Chinese and NA cultivars were noted for leaf and seed traits. Multivariate analysis captured 79% of the total genotypic variation among the 72 cultivars and was used to develop PS estimates. Cluster analysis of PS showed a much greater phenotypic diversity among Chinese than among NA cultivars and a striking distinctness between the two groups. The contrasting nature of Chinese and NA cultivars in this study is theorized to reflect that (i) the NA cultivars may trace to a subset of the Chinese cultivar genetic base, and/or (ii) Chinese and NA cultivars may have diverged phenotypically via breeder selection pressure. Cluster results here, based on PS, agreed roughly with previous cluster analyses, which were derived from pedigree analysis. The physical distinctness of NA and Chinese cultivars shows that introgression of Chinese cultivars into NA breeding should broaden NA germplasm's agronomic, morphological, and biochemical diversity. Introgression may be accomplished most effectively by avoiding matings of Chinese and NA cultivars from the same phenotypic cluster.