| Soybean [Glycine max(L.)Merr.] is an important oilseed crop in the world and an important source of vegetable oil and vegetable protein for humans.Soybean seed germination vigor traits are the basis for seedling establishment,a critical stage for improving soybean yield and quality.The vast majority of crop production relies on sown seeds,which are the ultimate measure of achieving high crop yields.Seed vigor has been found to be highly dependent on the stage of maturity,and varieties with high vigor seeds can increase crop yields by 20% to 30%.With the continuous development of China's agricultural mechanization,the requirements for seed seed quality are increasingly high,and high-vigor seeds are more suitable for production needs,which is important for improving soybean yields.Previous considers on quantitative trait loci(QTL)for seed vigor in soybean were basically from biparental segregating populations,and few reports from natural populations.Therefore,in this study,a total of 257 spring soybean released cultivar varieties(lines)and 104 spring soybean landrace varieties from northeast China were selected to build two natural populations.The seven vigor-related traits of germination rate(GR),germination vigor(GV),seedling fresh weight(FW),seedling length(SL),main root length(MRL),hypocotyl length(HL),and lateral root length(LRL)of identified seeds in two years(2018 to 2019)were also counted.In parallel,genetic variation and correlation analyses were performed for seed vigor phenotypes.The genomes of spring soybean varieties in northeastern China were examined using 175 pairs of SSR markers covering 20 chromosomes of soybean with polymorphisms to analyze the genetic diversity of spring soybean varieties and reveal the linkage disequilibrium characteristics of SSR markers in spring soybean varieties.The GLM program in TASSEL software was used for association mapping of vigor traits to further explore loci associated with vigor traits in spring soybean in northeastern China.The main results were as follows:1.Analysis of variance(ANOVA)was performed on the traits related to seed vigor in the two natural populations,and the differences between the varieties were found to reach a highly significant level.Seed vigor-related traits of both bred and local soybeans showed a continuous distribution,and six phenotypes(except hypocotyl length)of bred soybeans had higher values compared to soybean landrace varieties.Heritability in the broad sense of all vigor characteristics ranged from 62.19% to 95.43%,indicating that vigor traits were genetically stable;the coefficients of variation of their phenotypic traits ranged from 13.21% to 43.16%,indicating that northeastern spring soybean has wide phenotypic variation and great potential for selection.2.There was a rich genetic diversity of spring soybean varieties in northeastern China.A total of 844 allelic variants were detected,with an average of 4.82,variance of2 to 12,polymorphic information content(PIC value)of 0.45 and genetic diversity of0.50 on average.The number of elite alleles,genetic diversity and polymorphic information content(PIC value)of landrace soybeans were higher than those of released cultivar soybean,indicating that genomic genetic diversity in released cultivar soybean may have been reduced after long-term natural and artificial selection.3.According to the statistical results of STRUCTURE software,both soybean released cultivar populations and soybean landrace varieties populations were divided into three subgroups.In the released cultivar populations,62 accessions of Pop?,mainly from Jilin Province,81 accessions and 114 accessions of Pop? and Pop?,respectively,mainly from Heilongjiang Province.In the landrace soybean populations,and 41 accessions of Pop?,38 accessions of Pop?,and 25 accessions of Pop?.4.The results of the linkage disequilibrium analysis showed that there were more linkage disequilibrium loci in released cultivar populations than in landrace soybean populations.But the degree of linkage disequilibrium was higher in soybean landrace than in soybean released cultivar;the LD decay distances of soybean released cultivar and soybean landrace were 2.53(c M)and 1.46(c M),which showed that the LD decay distance of soybean landrace was shorter and the decay was faster.5.A total of 39 loci associated with vigor traits were detected in the soybean released cultivar populations and soybean landrace populations for two years,with a cumulative total of 110 loci(times)distributed on 19 chromosomes,of which 14 SSR loci were significantly associated with seedling fresh weight(FW),10 SSR loci were significantly associated with seedling length(SL),7 SSR loci were significantly associated with main root length(MRL),4 SSR loci were significantly associated with hypocotyl length(HL),11 SSR loci were significantly associated with germination rate(GR),9 SSR loci were significantly associated with germination vigor(GV),15 SSR loci were significantly associated with lateral root length(LRL).In the soybean released cultivar populations,a total of 15 identical loci were detected for two consecutive years,and the explanation rate for phenotypic variation was located from 4.19% to 14.30%,with the highest explanation rate for phenotypic variation for marker Satt303(14.30%in 2018 and 10.52% in 2019).In the soybean landrace populations,a total of 9 identical loci were detected for two consecutive years,and the explanation rate for phenotypic variation was located at 11.43% to 28.13%,with the highest explanation of phenotypic variation for the marker Sat?378(21.08% in 2018 and 28.13% in 2019),with more association of the same locus with multiple vigor traits in both populations.6.Based on the association analysis,a total of 52 and 27 elite alleles with positive effect were identified in the soybean released cultivar and soybean landrace populations,respectively,by further exploring the elite alleles of markers and corresponding materials that were jointly tested with vigor traits for two years.Among them Sat?256-236 bp and Sat?378-168 bp,Satt441-281 bp and Sat?378-156 bp,Satt329-262 bp and Sat?337-281 bp,Satt588-128 bp and Satt304-169 bp,Satt577-112 bp and Sat?378-168 bp,Satt413-196 bp and Sat?378-156 bp,Satt234-108 bp and Satt510-142 bp increased seedling fresh weight(FW),seedling length(SL),main root length(MRL),hypocotyl length(HL),germination rate(GR),germination vigor(GV),and lateral root length(LRL)most significantly,respectively,and corresponding typical carrier materials were Hefeng48 and Keshandajinhuang,Hefeng66 and Tiejiasilihuang,Hefeng44 and Longyoutai,Jiunong1 and Keshandajinhuang,Yufeng20 and Jiaohetianedan,Hefeng44 and Jiaohetianedan ? Hefeng51 and Baoxiandou.Allelic variants of the same marker were found to have either the same or different directions of phenotypic effects on different traits.In the two best cross combinations for improving seed vigor traits were identified,it was found that Suinong26,Hefeng51 and Keshandajinhuang were repeated in different cross groups,and these varieties could improve several vigor traits at the same time,to be verified in the next step. |
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