Genetic Variation And QTL Mapping Of Seed Storability In Soybean From Yangtze-huai River Valley

Soybean seed is rich in protein and fat,so it is easy to lose the vigor in natural storage condition during germplasm conservation.It is important to identify soybean germplasm with good seed storability and reveal its genetic basis for breeding elite cultivars.However,only a few studies on the genetics and breeding of soybean seed storability are available.In this study,the seed storability of a sample consisting of 375 soybean lines from Yangtze-Huai River Valley and 2 related RIL populations(ZYHD×M8206,LHFQD×M8206 containing 126 and 104 lines respectively)was investigated under natural aging and artificial aging test.Seeds stored in the active germplasm bank for 32-44 months(harvested in 2011 and 2012)were used for natural aging treatment,and seeds harvested in 2014 was used for artificial accelerated ageing tests.The genetic variation of the tolerance to storage of the populations was evaluated and lines with good seed storability were identified by using germination related traits.Moreover,QTL mapping for the seed storability was conducted using genome-wide association study(GWAS)and linkage analysis based on available SNP genotypic data,and some stable loci were identified for further genetic study and breeding utilization.The main results are as follows:1.The treatment of 45 ± 1℃ and 95± 1%RH for 5 days was found to be the optimum one for seed artificial aging according to pre-artificial aging experiments.The seed germination rate(GR),normal seedling rate(NSR),whole seedling length(WSL),seedling shoot length(SL),seedling root length(RL),fresh weight of normal seedling(FW),dry weight of normal seedling(DW)were selected as indicators for evaluation of seed storability of 375 lines under natural 328 lines under aging and artificial accelerated aging conditions.The average GR of seeds stored 3 and 4 years were 40.77%and 88.60%,and their range were 0.00%-100.00%,30.77%-100.00%respectively.The values of h2 of the GR were 87.62%,respectively.After artificial aging,the average relative seed germination rate(rGR)was 25.08%,ranged from 0.00%-95.56%,and h2 was 94.22%.It showed that there were significant genotypic differences among the tested lines,and existed large genetic diversity and selection potential.Total 31 and 25 lines with good tolerance to natural and artificial aging treatment were screened out respectively,and 4 of them performed good tolerance under the two aging treatments.After artificial aging,the seed vigor of two RIL populations was worse than that of the breeding lines.2.SNP markers were selected by using PLINK V1.07 to reveal the population structure by using ADMIXTURE V1.23 software,and it showed that the breeding line populations were consisted of 3 subpopulations.The same result was obtained using TASSEL 5.0 software based on 61788 and 62279 SNP markers for principal component analysis.Association mapping was conducted to detect linked markers with QTL for germination traits in the population based on MLM_PCA+K model.Using significant level-log10P≥3,a total of 100 and 148 SNPs were identified to be significantly associated with the 7 seed germination related traits under 3 or 4 years storage,and 40 and 46 QTLs were also screened out respectively.Among them,5 and 12 QTLs for GR,4 and 11 QTLs for NSR,respectively.Under Artificial accelerated aging,431 markers were found to be associated with storability,and a total of 101 QTLs were detected,Among them,13 QTLs for rGR and 15 QTLs for rNSR were found.To compare the mapping results of two aging methods,total 76 QTLs distributed on chromosome 1,3,4,7,8,9,10,11,13,15,16,18 and 20 were detected under both aging methods.More QTLs and markers were located on chromosome 9,11,13,17,18 and 20.3.The average GR of LM6 and ZM6 after three years storage were 79.60%and 79.87%,ranged from 38.78%-100.00%and 43.04%-100.00%,respectively.The broad-sense heritability were 53.27%and 56.76%respectively.After artificial aging,the values of relative germination rate(rGR)of two RILs were 25.62%and 14.37%,ranged from 0.00%-76.20%and 0.00%-90.70%,respectively.The values of h2 were 89.13%and 83.80%respectively.QTLs for seven germination traits of LM6 and ZM6 under natural and artificial aging treatment were mapped by Win QTL Cartographer VER 2.5 with high density genetic map which based on the method of composite interval mapping.Seting LOD>2.5,33 QTLs were detected for LM6 after three years storage.Among 4 QTLs for GR,LOD value of qGR-5-2 was considered as a major QTL with highest LOD value 5.07 and R2= 15.05%.Total 23 QTLs were detected for LM6 after artificial aging treatment.Among 5 QTLs for rGR,qrGR-17-2 was considered as a major QTL with highest LOD value 8.65 and R2= 22.64%.Seventeen QTLs were detected for ZM6 after three years storage.Among 3 QTLs for GR,qGR-5-1 was considered as a major QTL with highest LOD value 6.64 and R2= 16.76%.Sixteen QTLs were detected for ZM6 after artificial aging treatment.Among 3 QTLs for rGR,qrGR-18-1 was considered as a major QTL with highest LOD value 6.61 and R2=16.03%.There were 16 QTLs detected under both aging methods.According to the results of linkage analysis,the QTL on chromosome 5,17and 18 could be the priority loci for further study of seed storability in soybean.Combined with the results of association mapping,it also found that there are some common sites on chromosome 3,4,10,13,14,15,17,20.for example in 9645326 bp-11356351 bp of chromosome 17,there were commonly detected 4 QTLs,respectively qrRL-17-2 under artificial aging,qGR-17-1,qSL-17-2,qWSL-17-2 of LM6 undre artificial aging,which qrRL-17-2 detected more SNP markers,qGR-5-1 was considered as a major QTL with higher LOD value 4.44 and R = 15.08%.In summary,the resistance of storability of soybean is controlling by many QTLs,it is need to further study the molecular breeding methods based on genome-wide QTL information,a few relatively large effect and stable performance of QTLs can be used for further research.