Population Structure And Genetic Diversity Of A Core Collection Of Common Beans(Phaseolus Vulgaris L.)

Common bean(Phaseolus vulgaris)is one of the most important grain legumes in the world.It was originated in two centers of diversity and then gave rise to two genepools: the Mesoamerican genepool and the Andean genepool.Chinese common beans were introduced from the Americas,and they were spread rapidly from south to north in China and formed a great variety of common bean germplasm resources.By constructing a core collection of common beans to decipher the genetic structure and diversity of Chinese common bean is of great significance to the conservation,innovation and utilization of common bean germplasm resources.The specific goals of this study were to determine population structure and evaluate genetic diversity of a core collection of Chinese common bean by using three different types of markers in order to provide a theoretical reference for utilization and the effective excavation of high quality germplasm resources.This study obtained several main results as the following:1.Defined the population structure of Chinese common bean germplasm resourcesThe morphological markers classified all germplasm resources into six groups(Pop1,Pop2,Pop3,Pop4,Pop5,and Pop6).The germplasms of Pop1 and Pop2 characteristics typical of the Mesoamerican genepool,and the germplasms of Pop3 and Pop4 characteristics typical of the Andean genepool,the germplasms of Pop5 and Pop6 were inferred as introgression materials between the two genepools.The phaseolin markers divided all germplasm into two groups,corresponding to the Mesoamerican genepool and the Andean genepool,respectively.Intermediate type of phaseolin between two genepools wasn't found.SSR markers divided all germplasm into three subgroups(M1,M2,and A1).The subgroup M1 and M2 belonged to the Mesoamerican genepool,and A1 belonged to the Andean genepool.According to the results based on three types of markers,the materials of Mesoamerican genepool among Chinese germplasm resources accounted for 58% and the Andean genepool materials accounted for 42.0%.The above results confirmed that both the Mesoamerican and the Andean genepools were introduced in Cina,and the amount of the Mesoamerican genepool germplasms were more than the Andean genepool.2.Expounded the genetic diversity of Chinese common bean germplasm resourcesChinese common bean germplasm resources contained rich variation in morphological traits.A total of 175 variant types were detected in 24 phenotypic traits,and the average number of variant types was 7.29.Of which the color variation of seed was largest with 20 variant types.The variant types of stem types,pod-setting habit,shape of leaf and seed coat luster were the least,both of which were 2 variant types.The PIC(polymorphic information content index)value of germplasm resources based on morphological markers was 0.5772.There are abundant variant types of phaseolin,a total of 12 types of phaseolin were detected,with value of PIC was 0.7923.The results in phaseolin level indicated that the diversity of phaseolin in landrace is higher than cultivars or strains.In addition,the correlation analysis between phaseolin types and seed traits showed that there was a correlation between phaseolin type and seed size.The small seed germplasms usually with the phaseolin type of Sb,while the large seed germplasms usually with the phaseolin type of T.At the molecular level,931 variant types were detected among the core collection by using 116 polymorphic SSR markers,with an average allelic variation of 8.03 and PIC value of 0.5254.The results of morphological level indicated that the genetic diversity of the Andean genepool germplasm(PIC value was 0.562)was higher than that of the Mesoamerican genepool(PIC value was 0.4954).The results of protein level also showed the genetic diversity of the Andean genepool germplasm(8 phaseoiln types were detected,PIC value was 0.6027)was higher than that of the Mesoamerican genepool(4 phaseolin types were detected,PIC value was 0.5769).Meanwhile,the diversity of two genepools germplasm detected by using SSR markers suggested that the Andean genepool diversity(PIC value was 0.4119)was higher than that of the Mesoamerican genepool(PIC value was 0.3924).The results at the three levels were consistent.The above results illustrated that Chinese common beans undergone domestication in the process of adapting to various eco-climate types and formed genetic diversity-rich germplasm resources.The genetic diversity of landrace in Cinese common bean was higher than that of cultivars or strains,and the genetic diversity of the Andean genepool germplasm was higher than the Mesoamerican genepool.3.Comprehensive analysis of population structure and genetic diversity using three markers to ensure the comprehensiveness and accuracy of resultsComparing the clustering results of core collections using different types of markers demonstrated that the rate of consistency between morphological markers and phaseolin markers was 72.0%,and the rate of consistency between morphological markers and SSR markers was 70.0%.The rate of consistency between phaseolin markers and SSR markers was up to 92.1%.The results of analysis of population genetic diversity by different methods revealed that the genetic diversity detected by phaseolin was the highest(PIC value was 0.8098),the morphological detection was the second high(PIC value was 0.5772),and the diversity detected by SSR markers was the lowest(PIC value is 0.5257).There are differences in the accuracy of the three methods of analysis.The phaseolin markers can distinguish germplasm between two genepools,but it can't further study the subpopulation structure within the genepool.However,morphological and SSR markers can distinguish subpopulations very well and perform relationship analysis between subgroups.Therefore,the three methods complement each other and make the results more comprehensive and accurate.