Identification Of Drought And Salt-Tolerant Germplasm Resources In Wild Emmer And Genome-Wide Association Analysis

As the donor of A and B sub-genomes,wild emmer wheat has been an important germplasm and gene pool for genetic improvement of common wheat(Triticum aestivum L,2n = 6x =42,AABBDD).Wild emmer wheat(Triticum dicoccoides,2n = 4x = 28,AABB)is the wild species of tetraploid,as the direct ancestor of Triticum turgidum(2n = 4x = 28,AABB)and common wheat(Triticum aestivum L,2n = 6x = 42,AABBDD),which is domesticated and cultivated about 10,000 years ago,and plays an important role in the origin and evolution of common wheat.Furthermore,wild emmer wheat is also one of the invaluable wild resources for wheat genetic improvement and breeding due to its excellent characteristics such as salt tolerance,drought resistance,disease resistance,high content of trace elements in grains and high protein content,etc.In order to explore the excellent stress-resistant resources in wild emmer wheat germplasm,this study performed a preliminary evaluation the salt tolerance and drought resistance of wild emmer wheat and then,identify related genes or loci through genome-wild association analysis.The main results are as follows:1.Using 50 wild emmer wheat from originated region and 14 durum wheat from worldwide as the materials,we treated the plants at three-leaf stage using 150 mM NaCl as salt treatment and 18 traits were investigated after 1 month of treatment to calculate the salt tolerance index(STI).The results showed that on the whole,the average salt tolerance index(STI = 0.58)of wild emmer wheat was lower than that of durum wheat(STI = 0.64),but the variations of wild emmer wheat was higher than that of durum wheat,which showed that the genetic basis of wild emmer wheat was larger.According to principal component analysis,root length,root volume and root diameter were significantly correlated with STI,which could be used as the indicator for salt tolerance of wild emmer wheat.Based on all the traits,one extremely salt-tolerant wild emmer wheat material W77(STI = 0.97)and 6 wild emmer wheat materials with high salt tolerance were identified,which laid a material foundation for the genetic improvement of salt tolerance in wheat.2.Totally,79 wild emmer wheat genotypes were used for drought tolerance identification,using 19.2% PEG simulating drought environment and stress treat lasted for 1 month.Biomass was investigated and drought resistance index(DTI)was calculated.The results found that one strong drought-tolerance accession with the DTI value of 1.04.Combined with the STI and DTI values,4 genotype with strong drought resistance and salt tolerance were identified,they are W77,W81,W105 and W107.These materials can provide an important basis for the study of excavation and analysis mechanisms of drought-tolerant and salt-tolerant.3.A total of 113 tetraploid wheat accessions were genotyped using 90 K SNP chip,resulting in 55202 filtered SNP loci.Population structure analysis showed that there was obvious genetic divergences between wild emmer wheat and durum wheat.And as a cultivated species,durum wheat was subjected to stronger artificial selection effect.The genetic diversity of durum wheat was significantly lower than that of wild emmer wheat.4.Finally,genome-wild association analysis were performed using the SNP genotype and phenotypic traits from salt tolerance screening.Determine the general linear model(GLM)was found to be the optimal model by observing the relationship between the actual p value and the expected p value of each trait through the QQ diagram.Under CK,54 makers were found to associate with salt tolerance while 37 sites were identified under salt treatment.Furthermore,2 loci were significantly associated with salt tolerance index(STI).Additionally,15 loci were pleiotropic sites which involved in multiple traits.The identified SNP loci provided the powerful tool for fine mapping and molecular breeding for salt tolerance.The salt-tolerant and drought-tolerant germplasm resources and associated SNP marker loci identified in this study provided the important germplasms and tools for wheat drought and salt-tolerant breeding,and are of great significance for promoting genetic improvement and breeding of new varieties with elite drought-tolerance and salt-tolerance.