Evaluation And Genome-wide Association Study Of Drought Tolerance At Seed Germination Stage In A Yangtze-Huai Soybean Breeding Germplasm Population

Soybean[Glycine max?L.?Merr.]is is an important economic crop which is rich in oil,protein,mineral elements and beneficial phytochemicals.Drought is one of the major abiotic stress causing yield losses in soybean.The Yangtze and Huaihe are an important area of soybean production in China,where seasonal drought occurred frequently at sowing and germination stages.So it is important to screen and identify resistance resources and understand their genetic base for breeding drought-resistant cultivars.In this study,470 soybean lines of YHSBGP from Yangtze-Huai River Valley were used as material,under the simulate Artificial Drought Stress?15%PEG-6000?,data were recorded for 5 germination related traits viz.germination energy?GE?,germination rate?GR?,whole seedling length?WSL?,root length?RL?and seedling dry weight?SDW?were determined under the drought stress and the control.Based on the subordinative function value lines with good drought tolerance were identified.To discover QTLs for the drought tolerance in soybean,genome-wide association study?GWAS?was conducted by using 60510 single-nucleotide polymorphisms?SNPs?in TASSEL V 5.2.Some drought tolerance loci were identified and these loci could explain the excellent allelic variation of elite germplasm.The main results were as follows:1.Screening and evaluation of the soybean germplasm at germination stage for drought toleranceAccording to pre-artificial aging experiments,the artificial drought stress test was established,that is under 15%PEG-6000 for 5 days,on the sixth day germination related traits:germination energy?GE?,germination rate?GR?,whole seedling length?WSL?,root length?RL?and seedling dry weight?SDW?were measured.The results showed that the germination related traits without drought stress had higher mean values,and smaller variations than those measured under the control.An analysis of variance?ANOVA?indicated significant?P<0.01?genetic variation for all traits in drought tolerance treatment and the control.The correlation analysis showed that,there was extremely significant positive correlation between all the traits,which reflected the inherent linkages between these indicators.Based on the subordinative function values of 5 traits,the 470 accessions were divided into 5 grades;14?accounting for 2.98%of whole sample?and 61?accounting for 12.98%of whole sample?lines were identified with high drought tolerant and high drought susceptibility,respectively.2.QTL mapping for germplasm at germination stage for drought toleranceThe major allele frequency amplitude was 0.5000-0.9489,with an average value of 0.7794;the genetic diversity value range were 0.0969-0.5000,with an average of 0.3109;the polymorphism information content average was 0.2542,ranged from 0.0922 to 0.3750;the analysis of genetic diversity indicated that there was abundant genetic variation in soybean germplasm from YHSBGP.A total of 470 lines were divided into three subpopulations according to population structure analysis,in subpopulation 1?including 262 accessions?,most soybean accessions were derived from the main parent 86-4;in subpopulation 2?including 157 accessions?,most soybean accessions were descended from the parent 88-48;in subpopulation 3?including 51 accessions?,most soybean accessions were derived from the main parent Tong Dou and Liu Feng,the principal component analysis and the neighbor-joining tree analysis showed consistent results with population structure analysis.The analysis of linkage disequilibrium?LD?showed that the values of R2 and D' in 0.90-1.00 were 8.66%and 58.66%,respectively;the decay of linkage disequilibrium?LD?was approximately 500 kb.A total of 3 SNPs were identified to be significantly associated with 5 traits under significant level-log10P?4.78;a total of 103 SNPs were identified to be significantly associated with 5 traits under significant level-log10P?3.50,detected locis were mainly distributed in soybean genome chromosomes of 3,4,5,9,10,11,12,13,16,17;of which 6 locis were identified to be significantly associated with RWSL and RRL;according to previous studies that the Gm10₃8907922,Gm10₃8920843 and Gm10₃8921029 were nearly close to drought resistance related sites satt478 and sat581.3.Analysis of elite allele for germplasm at germination stage for drought toleranceThe effect of allelic variation of SNP markers,which were significantly correlated with germination traits,some elite alleles with highest effects were selected.Among them,6 positive alleles associated with relative germination energy;7 positive alleles associated with relative germination rate;21 positive alleles associated with relative root length.Twenty specific lines with maximum values of each trait were selected to identify their allele composition.High drought tolerance accessions Ai/118-1 with 5 elite alleles associated with relative germination energy and 94-16/IA2077-3 with 15 elite alleles associated with relative root length were sreened out.That provide theoretical and practical guidance for breeding.