Qtl Mapping Of Salt Tolerance In Soybean RIL Population NF2002

Soybean[Glycine Max（L.）Merr.]is an important oil crop,due to its richment in high-quality oil,protein,isoflavones,dietary fiber,etc.Soybean has been widely utilized in food,feed and industry.However,soil salinization has become one of the main soil factors limiting soybean yield.Salt stress is mainly caused by Na Cl stress.Cultivated soybean plants will die when soil salinity exceeds 5 dsm^-1.Soybean salt-tolerance related traits are complex quantitative traits and controlled by multiple genes.Therefore,it is of great significance to identify the loci and genes controlling soybean salt-tolerance,which is important for soybean salt-tolerance breeding program.In this study,the Salt Tolerance Rating（STR）of PI595843（PI）and Wuhe Qi soybean（WH）,which are the parents for a population（NF2002）of soybean Recombinant Inbred Line（RIL）,was evaluated.It was found that PI was an extreme salt-tolerant variety with salt-tolerance level 1.4,while WH was a salt-sensitive variety with salt-tolerance level 4.0.There was a significant difference in salt-tolerance between these two parents,therefore their derived RIL population was suitable for QTL mapping of salt tolelrance.Salt tolerance traits were investigated and QTL mapping was performed in 295 recombinant inbred lines derived from PI and WH.The main results are as follows:1.The two parents of soybean RIL population NF2002 and two reference soybean varieties were evaluated for salt tolerance.Salt Tolerance Rating（STR）and the Ratio of Relative Water Content(RWC/R=RWC_treatment/RWC_control)were used as indicators for salt tolerance evaulation.The results showed that the STR of soybean reference varieties Lee 68and Williams 82 was 1.1 and 4.5,and their RWC/R values was 0.81 and 0.41,respectively.For the two parents of soybean RIL population NF2002,PI and WH,their STR was 1.4 and4.0,and their RWC/R was 0.79 and 0.45,respectively.When WH wilted and died under salt stress,PI were still alive.Therefore,evaluation and QTL mapping of salt tolerance was further carried out in the F_2:8 RIL population derived from the cross of PI and WH.2.The salt-tolerance of soybean RIL population NF2002 was investigated and the phenotypic data was analyzed.Salt tolerance of soybean RIL population NF2002 was evaluated using STR and RWC/R.The experiment was repeated three times in 2019,2020and 2021,respectively,and the heritability was calculated based the variance analysis using SAS software.There was significant difference in salt tolerance between soybean lines and different years.The broad-sense heritability of STR and RWC/R was 79%and 69%,respectively,and STR showed a significant negative correlation with RWC/R（r=-0.84,P<0.001）.3.Mapping salt tolerance QTL in soybean RIL population NF2002.QTL analysis was performed using Windows QTL Catographer version 2.5（CIM model）.A total of 11 QTLs controlling STR and 12 QTLs controlling RWC/R,were distributed on seven different soybean chromosomes（Chr）:Chr.6,Chr.7,Chr.9,Chr.11,Chr.16,Chr.18 and Chr.20.Five QTL loci were repeatedly detected by both STR and RWC/R.Compared with previous studies,the Gm06G4.94-9.93 genomic region on Chr.6 is a new salt-tolerant QTL cluster that has not been reported before.In this region,7 QTL loci were detected,of which 3 loci were detected by both STR and RWC/R:q STR06.2,q STR06.3 and q STR06.4 explained9.35%,9.89%and 10.19%of the phenotypic variation of STR,and 5.97%,6.09%and 8.29%of the phenotypic variation of RWC/R,respectively.q RWC/R06.2（8.73 Mb-9.9 Mb）detected by RWC/R overlaps with q STR06.5（8.61 Mb-9.22 Mb）detected by STR,which explained 9.99%and 11.81%of the phenotypic variation in RWC/R and STR,respectively.The q RWC/R07.1 locus on Chr.7 explained 8.08%of the phenotypic variation of RWC/R.Compared with previous studies,this is also a new salt tolerance QTL.A QTL cluster located on Chr.18 Gm18G54.47-57.46 overlaps with the previously reported salt-tolerance QTL region,including 4 QTL detected in this study.Among them,q RWC/R18.2,q RWC/R18.3 and q RWC/R18.4 explained 8.6%,8.54%and 8.00%of the variation in RWC/R,respectively,and q RWC/R18.2 and q RWC/R18.4 were detected by both STR and RWC/R.4.The candidate genes were screened for the three salt-tolerant QTL regions.There are 115 genes in the following three QTL regions:two major QTLs on Chr.6（accounting for 10.19%and 11.81%of the STR variation,respectively）,and one QTL on Chr.18detected by both STR and RWC/R.The GO functional annotations of these 115 genes were classified,and 43 of them were found to be related to salt tolerance.Based on the functions of Arabidopsis homologous genes,12 genes may be involved in plant tolerance to salt stress.Among them,nine genes were highly expressed in soyben leaves or roots,which could be further studied to investigate their roles in soybean tolerance to salt stress.