Identification Of Salt Tolerance And Association Analysis With SSR Markers In Fraxinus

China is a country with serious soil salinization.It is the focus of current research to cultivate salt-tolerant plants suitable for saline-alkali land growth.As an excellent afforestation and garden tree species in the northern saline-alkali region,it is beneficial to promote ecological protection and high quality development of the saline-alkali region to improve its stress resistance and explore its salt-tolerant gene to breed new salt-tolerant varieties in White wax.In this study,173 samples of White wax collected from nine provinces of China were used as research materials.After salt stress treatment in field,its salt tolerance was identified and evaluated comprehensively.Then genotypes were identified and SSR markers were used for genetic diversity analysis,genetic structure analysis and association analysis,so as to provide theoretical basis for White wax salt tolerance breeding.The main results are as follows:（1）Electrical conductivity（EC）level,chlorophyll（Chla and Chlb）content,carotenoid（CAR）content,superoxide dismutase（SOD）activity,malondialdehyde（MDA）content,catalase（CAT）activity,Peroxidase（POD）activity,soluble protein（SP）content were measured in 173 White wax germplasms.The results of one-way ANOVA show that the variation of the 9 salt tolerance physiological indexes reach a very significant level（P<0.001）,and the coefficient of variation ranged from 57% to 261.19%.The degree of variation is large,and the screening of salt-tolerant germplasm can be carried out and physiological indexeassociation analysis.The results of correlation analysis show that there are 20 pairs of extremely significant（P<0.01）or significant（P<0.05）correlations among the 9 salt tolerance physiological indexes,and the salt-tolerance physiological indexes are closely related,which can be used as indicators for the screening of salt-tolerant germplasms.（2）Cluster analysis and membership function analysis were used to comprehensively evaluate the salt tolerance of 173 White wax germplasms.The classification results of salt tolerance grades show that DS1,DT21 and DT24 are salt-tolerant germplasms,CP2,CP4,CP5 and LSY8 are moderate salt-tolerant germplasms,and 166 germplasms including BJ02,BJ3,BJ04 are salt-sensitive germplasms.（3）Amplification in 173 White wax germplasms using 14 pairs of SSR primers,the results show that the 14 pairs of primers produce a total of 91 alleles,the number of effective alleles is 2.672（1.310～5.071）,the diversity information index is 1.138（0.505～1.867）,and the polymorphism information content is 0.527（0.221～0.777）.Based on SSR molecular markers,the genetic diversity of White wax germplasms population is analyzed.The expected heterozygosity between populations is 0.528（0.435～0.639）,the observed heterozygosity is0.557（0.425～0.633）,the diversity information index is 0.977（0.780～1.224）,and the polymorphism information content is 0.593（0.534～0.680）.（4）The population structure of White wax germplasm was analyzed,and the results show that the natural population is divided into 3 and 2 subgroups under UPGMA clustering and Bayesian clustering,respectively,and the obtained Q values are all higher than 0.85.The genetic components are relatively simple.（5）Linkage disequilibrium analysis was performed on SSR molecular markers.The results show that when D’≥0.5 and P<0.01,there are 18 pairs（20%）of paired loci,and the linkage disequilibrium coefficient is between 0.05 and 1,with an average value of 0.16,the LD value of the tested White wax germplasm is relatively small.（6）The association analysis of 9 salt-tolerance physiological indexes of White wax and SSR molecular markers was carried out.Under the general linear model（GLM）,there are 8markers with extremely significant correlation（P<0.01）,with an average contribution rate of22.34%.Under the mixed linear model（MLM）,there are 5 markers with extremely significant association（P<0.01）,with an average contribution rate of 21.68%.The MLM model is selected as the optimal model,and the markers 92,167,202,208 and 213 are closely related to the salt-tolerance traits of White wax.And marker 202 is an important association site for the further study.