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Soybean is an important economic crop in the world, which provides plant protein, oil and a variety of active substances beneficial to human health. In order to comprehensively identify the quality characters of soybean resources abundant in China, 16 kinds of seed quality traits of 520 soybean germplasms in Huang-Huai-Hai ecoregion were evaluated in 6 environments across 2 years with reference to the national standard method. The results showed that the genetic variations of the tested seed quality traits were abundant in the soybean germplasms, and the variation coefficients of isoflavone and tocopherol contents were relative high, while the variation coefficients of protein, oil and fatty acid components were relatively low. Meanwhile, there were significant correlations among the 16 seed quality traits. Principal component analysis showed that the 16 quality traits could be attributed to 5 principal components. Based on the results of principal component analysis, 520 germplasms could be divided into 3 categories by cluster analysis with significant differences. Based on the above results and high stability coefficient analysis, 35 germplasms with multiple or single elite seed quality traits were screened out, which provided important resources for genetic improvement of seed quality traits in soybean. [ABSTRACT FROM AUTHOR]

Symbiotic nitrogen fixation (SNF) in legume crops plays a crucial role in world sustainable agriculture. To analyze the genetic basis of SNF in soybean, a natural population composed of 267 typical germplasms genotyped with 5403 SNP markers was inoculated with CCBAU45436, an elite rhizobium strain from China. Eleven traits related to SNF were evaluated under greenhouse and field conditions, and a genome-wide association study (GWAS) was conducted. In total, 20 SNP loci (consisting of 38 SNP markers) that were significantly associated with 11 SNF-related characteristics were identified on eight soybean chromosomes. Three SNP loci located on chromosome Gm17 were associated with shoot nitrogen concentrations in the two environments. Two other SNP loci located on Gm17 in the adjacent region were associated with high nodule numbers and nodule fresh and dry weights. Moreover, the elite alleles and genotypes were selected based on the phenotypes of different groups, which further demonstrated the reliability of these associated SNP markers. Other colocalized SNP loci linked with different SNF traits were also detected. More importantly, some candidate genes found at the associated SNP loci showed different expression levels between the different developmental stages of soybean nodules, two of which were further verified by qRT-PCR results. These SNP loci and candidate genes could be applied in marker-assisted selection in breeding or map-based gene cloning in soybean for future genetic improvement. [ABSTRACT FROM AUTHOR]