Identification And Association Analysis Of Drought Tolerance Resources In Soybean Seedling Stag

Soybean is an important grain and oil crop.As the main source of high-quality protein,soybean has great potential for development.Our demand for soybean is large,but domestic soybean supply capacity is weak,mainly relies on imports,external dependency is up to 84%,increasing soybean output is important for ensuring our food safety production.Soybean is the most sensitive crop to water shortage,which requires higher water quantity in seedling stage.Due to poor irrigation conditions,drought and other factors in spring soybean producing areas,the water shortage in soybean seedling stage affects the growth and development of soybean seedlings,resulting in a decline in yield.It is of great significance to identify and analyze drought-tolerant resources at seedling stage,screen drought-tolerant germplasm resources,and correlate drought-tolerant traits with markers at seedling stage to provide theoretical guidance for the breeding of drought-resistant varieties of soybean.In this study,eight drought-tolerant traits,including RHW,RRFW,REW,RGR,RCFW,REL,RGE,RHL were selected to identify drought-tolerant resources in 332 soybean varieties.Genome-wide association analysis of drought tolerance traits in soybean seedlings was conducted using 30591 SNP markers.The main results are as follows: 1.Identification of drought tolerance resources in soybean Seedling stage Descriptive statistics were conducted on 332 drought tolerance related traits in soybean seedling stage.The coefficient of variation was between 11.17% and 42.67%,indicating that there was extensive genetic variation in each trait.The highest genetic diversity of drought tolerance index was 1.89 relative to epicotyl length.The 8 drought tolerance related traits showed significant correlation with each other except for the relative germination potential and relative germination rate,which had low correlation with other traits.The cluster analysis showed that 332 soybean germplasm could be divided into two groups,the first group had 314 soybean germplasm and the second group had 18 soybean germplasm.The second group had better drought tolerance than the first group.The D values of 332 soybean germplasm were calculated based on the first three PCA methods,and 18 extreme drought tolerant varieties were obtained,accounting for 5.42% of the total number of varieties.Among them,Jiunong No.4 had the best drought tolerance,which could provide parent materials for breeding high-quality drought-resistant soybean varieties at seedling stage.2.Genome-wide association analysis of drought tolerance in soybean seedlingsResults of genetic diversity analysis: A total of 248939 alleles were detected,with an average genetic diversity index of 0.410,PIC mean of 0.347 and MAF mean of 0.698.Population structure analysis of 322 soybean germplasm were divided into 5 subgroups,including 78,67,73,62 and 52 soybean germplasm,respectively.The results of linkage unbalance analysis show that the LD attenuation distance is 118 kb when r~2 decreases from 0.7 to 0.35.GLM model combined with 30591 SNP markers was used for association analysis.A total of 349 SNP markers were associated at the significant level of-Log10(P)≥3.The phenotypic variation interpretation rate of a single SNP locus ranged from 10.70% to 27.80%,distributed on 20 chromosomes of soybean.Forty-four of the tags were associated twice.The site ss715622311(Gm15)was found to be significantly correlated with drought tolerance at seedling stage of soybean.This site was significantly correlated with RGR and RGE,and-log10(P)=15.68,with an explanatory rate of phenotypic variation of 12.37%,which could provide theoretical basis for drought tolerance breeding of soybean.3.Candidate gene screening and functional annotationA total of 433 candidate genes were found to be significantly related to drought tolerance at seedling stage of soybean,among which 107 candidate genes were associated multiple times,Gene function is related to enzyme activity,protein processing and degradation,metal ion binding,etc.Glyma.15g253100 was C3 HC type zinc finger protein.Glyma.15g253200 was associated with negative regulation of protein phosphatase inhibitor activity and protein dephosphorylation.Glyma.18g074200 was associated with the expression of CBL.Glyma.19g230200 was concentrated in the protein serine/threonine phosphatase activity pathway.Glyma.10g015900 was enriched in glycosyltransferase.Glyma.15g134400 is involved in lipid binding.