Identification And Genetic Dissection Of Elite Lines With Good Seed Quality And Drought Tolerance In A Yangtze-Huai Soybean Breeding Germplasm Population

Crop breeding line is often derived from crosses between core parents and a plenty of elite germplasm, and can retain many specific genes adaptive to local environment condition and introduce many new genes, so it is one of the major parent types in a crop breeding program. On the other side, association analysis has already successfully used to map QTL of interesting traits in plant, and can be used as a new way to reveal the genetic base of elite crop germplasm resources.High protein and oil content are the important soybean breeding traits in Yangtze-Huai valleys. Furthermore, drought tolerance at germination stage is helpful to resist the harmful environment for soybean. In the present study,309lines from the crosses between four core parents with high quality and many domestic and exotic germplasm were selected to establish a Yangtze-Huai soybean breeding germplasm population (YHSBGP). Seed protein content, oil content and PEG-simulated drought tolerance at germination stage were investigated to reveal their genetic variation and identify elite lines. The InDel molecular markers were also used to map QTL for these traits by MLM_Q+K model of association mapping. Elite alleles of the associated marker loci and their carriers were also identified. The main results are as follows:1. In YHSBGP population, there were significant differences of four traits (protein content, oil content, relative germination energy and relative germination rate under PEG treatment) among the breeding lines according to the results of analysis of variance. The heritability of protein content, oil content, relative germination energy and relative germination rate were57.97%,62.21%,66.81%,68.54%, respectively. The protein and oil content was ranged from39.33%to50.25%and15.56%to21.80%, respectively. It indicated that the YHSBGP population had greatly genetic variation. The specific lines with protein content higher than46.00%, oil content higher than20.50%, total content of protein and oil higher64.50%, relative germination rate higher than80.00%were selected as elite lines.2. Total470alleles were detected by228InDel markers in YHSBGP population. The average allele number per locus was2.1, the average PIC value was0.22, and the gene diversity average value was0.26. Forty InDel markers were used to analyze the population structure based on math model by STRUCTURE software. The result indicated that there were four sub-populations in this population. All InDel markers were used to analyze the degree of linkage disequilibrium in the population. As a result,91.36%of r2values were between0to0.2, and66.06%of D’values ranged from0to0.5.3. Association mapping was used to detect related QTL for protein and oil content of five environments in two years based on MLM_Q+K model, the results indicated that there were total59significant loci (time) for protein content and98significant loci (time) for oil content. Among them, total12and32were extremely significant loci for protein content and oil content, respectively. Total11and18loci for protein content and oil content can be detected in more than2environments respectively and21loci have been reported in previous studies. The loci Gm11sv431、Gml8sv704and Gm14sv509were pleiotropic to both protein content and oil content. Total15and13significant marker loci were detected to be associated with relative germination energy and relative germination rate under PEG treatment respectively.4. Alleles of the loci significantly associated with seed quality and drought tolerance at germination stage were analyzed and some elite alleles with highest effects were selected. The results indicated that there were12positive elite alleles for protein content,13positive elite alleles for oil content and16positive elite alleles for drought tolerance at germination stage. Twenty lines with maximum phenotypic values of each of three traits were selected, and the constitution of positive alleles and their genetic relationship based on the molecular markers were also analyzed. These elite alleles and elite lines could be applied in developing new varieties with good seed quality and drought tolerance in soybean.