Marker Development And Utilization Of Salt Tolerance Gene GmSALT3 At Seedling Stage And QTL Mapping For Salt Tolerance At Emergence Stage In Soybean

Salinity is a severe environmental factor affecting crop production.Screening salt tolerant soybean（Glycine max）germplasm is of great valuable for the utilization of salinized soil in major soybean production area.In this study,the genomic variation information of the salt tolerant gene GmSALT3 in soybean was used to develop functional molecular markers.Soybean cultivars new breeding lines in China were analyzed using these markers.An effective method for screening salt tolerant germplasm and mapping Quantitative trait loci（QTL）at emergence stage was developed.the research provided materials and molecular markers for future soybean breeding.The main results are as follows:1、Development and Utilization of Functional Markers of Salt Tolerance Gene GmSALT3 at Seedling StageFive haplotypes have been observed in Chinese soybean landraces in our previous research,of which H1 is a salt tolerant haplotype and H2-H5 are salt-sensitive haplotypes.Here,we developed five functional moleculaer markers of GmSALT3.Insertion and deletion（Indel）marker Pro-Ins was designed to distinguish H1 and H2 haplotypes from H3–H5.Indel marker H2-Ins and H5-Del was designed to distinguish H2 and H5 and other haplotypes,respectively.The Cleaved amplified polymorphic sequence（CAPS）marker H3-MboII and H4-NlaIII was developed to distinguish H3 and H4 from other haplotypes,respectively.Five haplotypes were identified in 706 Chinese soybean cultivars.Regionally,four of the five haplotypes were observed in the Southern ecoregion（SR）and five were found in both the Huanghuaihai（HHR）and Northern ecoregions（NR）.Changes in allele frequency showed that the salt-tolerant haplotype,H1,gradually decreased in NR and increased in HHR,while the sensitive haplotype,H2,increased in NR and HHR since the 1970s.Tolerant haplotype H1 and sensitive haplotype H2 were dominant haplotypes in NR,while H1 was the predominant haplotype in HHR and sensitive haplotype H5 was most frequently found in SR soybean cultivars.Evaluation of the 536 modern Chinese breeding lines showed that 186 salt-tolerant lines were all of the H1 haplotype,and among the remaining 350 salt-sensitive lines,two were H1,220 were H2,one was H3,and 127 were the H5 haplotype.The identification efficiency of salt tolerant and salt sensitive germplasm was 98.9%and 100%,respectively.These results revealed that allelic variations in the gene is associated with seedling-stage salt tolerance in soybean breeding lines.Therefore,the markers have great potential for use in marker-assisted soybean breeding programs.2、A Screening Method to Identify Salt Tolerant Soybean at Emergence StageIn order to select salt tolerant soybean,a screening method was developed by using six soybean accessions,named Zhonghuang35（ZH35）,Zhonghuang39（ZH39）,Williams82（W82）,Tiefeng8（TF8）,Peking（Pek）and NY27-38.Seeds were grown in vermiculite and treated with 0,100 and 150 mmol L^-1NaCl solution.Compared with the control,seedling rate（SR）,plant height（H）,fresh weight of shoot and root（FWS and FWD）,dry weight of shoot and root（DWS and DWR）decreased significantly under 150not 100 mmol L^-1 NaCl treatment for 15 days,and significant difference among varieties were observed.Therefore,150 mmol L^-1 NaCl was suitable to identify salt tolerant soybean at emergence stage.The indicator of salt tolerance index（SI）and salt tolerance coefficient（ST）were significantly correlated with the salt tolerance.The indicator of salt tolerance index is non-destructive and does not require planting control.This physiologically based selection technique is time and labor saving for improving the efficiency of salt tolerant germplasm identification.Seventy-seven soybean resources were screened,in which nineteen highly tolerant（1 grade）and twenty-one tolerant soybean（2 grade）were identified at emergence stage.Among them,twenty-three germplasm showed salt tolerant（1 grade）at seedling stage.This effective screening method will be useful for identification of salt tolerant soybean germplasm.3、QTL Mapping for Salt Tolerance at Emergence Stage in SoybeanA mapping population of 142 F₇ families,derived from a cross between salt tolerant soybean variety Zhonghuang39 and salt sensitive wild soybean（Glycine soja）NY27-38 were used to map salt tolerance QTLs.The linkage map of this F₇ population,covering 2350.79 cM,with an average interval of 12.56 cM,consisted 202 Simple sequence repeats（SSR）markers.QTL mapping was conducted using Inclusive Composite Interval Mapping,two QTLs for salt tolerance at emergence stage in soybean were identified,which were mapped on chromosomes 6 and 14,respectively,with LOD scores ranging from 2.21 to 18.27,which explained 2.06%to 21.01%of total phenotypic variation for salt tolerance at emergence stage.The detection of salt tolerance QTLs will provide usefull informations for future gene cloning.