Analysis Of Genetic Diversity And Sensitivity To Defoliant Of Upland Cotton Germplasm Resources In Southern Xinjiang

Cotton is an important natural fiber crop and one of the important cash crops in China.With its unique regional environment and resource advantages,Xinjiang has become the main cotton producing area in China.In order to reduce labor costs and tap the potential of increasing income,machine-picked cotton has been rapidly developed and widespread in Xinjiang,especially in the corps.Although machine-picked cotton reduced the costs,it led to a serious decline in fiber quality.Therefore,it is the fundamental for the cotton industry to cultivate varieties with excellent quality and sensitive to defoliant.In this study,phenotypic traits and SSR molecular markers of 90 Southern Xinjiang germplasm resources were used to study the genetic diversity and defoliant sensitivity of upland cotton germplasm resources.This study provides references for the utilization of upland cotton germplasm resources in Southern Xinjiang and the breeding of new upland cotton varieties suitable for machine picking.The main findings are as follows:1.Phenotypic traits of 90 upland cotton germplasm resources in Southern Xinjiang were identified for2 years,and the results showed that the variation coefficient of phenotypic traits ranged from 0.82-26.55%,with an average variation coefficient of 10.00%,and the diversity index ranged from 1.92-2.07,with an average of 2.02.The results showed that the phenotypic traits of upland cotton germplasm resources in Southern Xinjiang had great genetic diversity.The results of phenotypic traits clustering showed that the germplasm resources of upland cotton in Southern Xinjiang could be divided into 2 groups,including 36 and 54 materials,respectively.The two groups each can be divided into 3 subgroups,and the phenotype of each subgroup have different characteristics,which can provide materials with different characteristics for the cultivation of new upland cotton varieties.2.Genetic diversity analysis of the 22 pairs of primers with clear bands and polymorphism selected from 180 pairs of SSR primers showed that the average value of genetic diversity was 0.2817,and the variation range of PIC was 0.0220-0.5388,with an average value of 0.2497,indicating that there was a certain genetic diversity of upland cotton germplasm resources in Southern Xinjiang.Cluster analysis and population Structure analysis were carried out by NTSYS,Powermarker and Structure,respectively.The results showed that the genetic basis of upland cotton germplasm resources in Southern Xinjiang was relatively simple.The clustering results of NTSYS based on similarity coefficient were different from those of phenotypic traits,while the results of Powermarker and Structure were consistent with the clustering results of phenotypic traits.3.Field experiments found that different materials had different responses to defoliant,and the defoliation rate at day 4-7 could be used as an evaluation index of defoliant sensitivity.After the application of defoliant,the defoliation effect of fruit branches leaves was the best,followed by foliage leaves,and the defoliation effect of main stem leaves was the worst.Then JP-11(10),Xinluzhong 2(33),Xinluzhong 29(41),Junmian 1(69),Zhong414(82)and Zhongmian 641(89)that particularly sensitive to defolderant were screened out.Phenotypic traits and SSR molecular markers showed that upland cotton germplasm resources in Southern Xinjiang could be divided into 2 groups and have narrow genetic basis.It was found that upland cotton germplasm resources in southern Xinjiang had a large variation coefficient of phenotypic traits andrich genetic diversity.However,SSR molecular markers indicated that there was a certain genetic diversity in the germplasm resources of Upland cotton in Southern Xinjiang.Field experiments showed that the sensitivity of defoliants varied among different varieties and typical materials sensitive to defoliants were screened out.This experiment provides a theoretical basis for evaluating and utilizing of the upland cotton resources in Southern Xinjiang and a reference for cultivating new varieties suitable for machine harvesting.