Genome-wide Association Study Of Mixed Saline-Alkali Tolerance In Soybean At Seed Germination Stage

Soybean(Glycine max(L.)Merr.)is one of the major oil crops and provides edible oil and abundant protein for human beings.However,saline alkali stress is an important disadvantage factor affecting soybean yield and quality.Therefore,identification and understanding the genetic architecture for soybean saline alkali stress tolerance is crucial in developing saline-alkali tolerant soybean cultivars.Although a lot of research progress has been made in the exploration and genetic analysis of soybean,the molecular mechanism of saline-alkali tolerance in soybean is still unclear.And there are few studies on the tolerance of soybean germplasm to mixed salt-alkali.In this study,281 soybean varieties(lines)were treated with 60 mmol / L mixed saline alkali solution during seed germination.The seven morphological indexes such as germination energy,germination rate,seedling length,root length,seedling fresh mass,root fresh mass and root dry mass were used to evaluate the salt-alkali tolerance of soybean germplasm.Meanwhile,according to the SNP markers information,the genetic composition of salt-alkali tolerance was analyzed by genome-wide association analysis.The excellent allelic variation and carrier materials were also explored.The main results were as follows:1.Identification of mixed saline-alkali tolerance of 281 soybean germplasm at seed germination stage281 soybean germplasms were treated with 60 mmol/L mixed saline-alkali solution at seed germination stage.Meanwhile,distilled water was used as control treatment.7 indicators namely germination energy,germination rate,seedling length,root length,seedling fresh mass,root fresh mass and root dry mass were evaluated.Based on the salinealkali tolerance coefficient of each indicator,the principal component analysis and subordinate function value method were jointly applied to comprehensively evaluate the tolerance of the tested germplasms to mixed saline-alkali stress.The results showed that mixed saline-alkali stress inhibited seed germination and growth of early seedling.Tolerance of 281 soybean germplasms to mixed saline-alkali stress was different and divided into five categories.Among them,there are 7 extremely mixed saline-alkali tolerance materials,accounting for 2.49%;20 mixed saline-alkali tolerance materials,accounting for 7.12%;135 medium mixed saline-alkali tolerance materials,accounting for 48.04%;103 mixed saline-alkali sensitive materials,accounting for 36.65% and 16 extremely mixed saline-alkali sensitive materials,accounting for 5.69%.2.GWAS for mixed saline-alkali tolerance in soybean at seed germination stageAccording to the phenotype data,combined with SNP markers covering the whole genome,the mixed linear model(PCA + K)and general linear model(GLM)in the software TASSEL V 5.2 were used to analyze the genetic composition of salt-alkali tolerance by genome-wide association analysis.The results showed that there were 268 SNP markers associated with 8 traits,which distributed on all 20 chromosomes of soybean.In particular,some chromosome regions,38.1-38.6 Mb of chromosome 5,6.8-7.8 Mb of chromosome 16,28.3-30.8 Mb of chromosome 16 and 22.4-23.6 Mb of chromosome 17 were associated with multiple traits,which could be used as important loci for gene cloning and molecular assisted breeding.3.Analysis of elite allele for germplasm at germination stage for mixed saline-alkali toleranceAccording to the GWAS results for salt-alkali tolerance,the significant correlation SNP markers with high effects value for different trait were screened out,furthermore,the distribution characteristics of these alleles in extreme materials were analyzed.And 9 alleles associated with relative root length,12 alleles associated with relative seedling length,5 alleles associated with relative root fresh mass,11 alleles associated with relative seedling fresh mass,7 alleles associated with relative root dry mass,7 alleles associated with comprehensive evaluation D-value were selected.In conclusion,the tolerance of mixed saline-alkali tolerance of 281 soybean germplasm at seed germination stage was identified.The genetic composition was dissected by genome-wide association analysis,and some important chromosome regions associated with multiple traits were excavated.These results could provide useful information for salt and alkaline tolerance breeding of soybean.