Screening of SSR markers associated with protein content in whole plant of forage soybean

Increasing the protein content of the whole plant is the most important breeding goal in forage soybean. To screen for effective molecular markers that can be used in the breeding of high protein content in forage soybean, 55 core germplasm resources were selected as the tested materials in this study. Then, 40 pairs of SSR markers related to protein content reported both at home and abroad were used to analyze the genetic diversity and population structure of the tested materials. The correlation between protein content and selected markers was analyzed in whole soybean plant with a GLM (general linear model) and MLM (mixed linear model) using Tassel 2.1 software. The results showed that 21 of the 40 SSR markers had high polymorphism and good repeatability, so were selected for further study. A total of 118 alleles were detected in the population of the 21 SSR markers, and the number of alleles (Na) varied from 3 to 10, with an average of 5.6. From the results of genetic similarity UPGMA cluster analysis, 55 materials could be divided into groups Ⅰ, Ⅱ, and Ⅲ. Four subgroups (POP1, POP2, POP3 and POP4) could be created according to genetic structure analysis using Structure 2.3.4 software. The classification results of the two methods were different but basically similar. Six SSR markers were significantly associated with the protein content of the whole plant, which can be used to breed for a high protein content via the molecular-marker-assisted selection in forage soybean.