Germplasm Population Structure Analysis And Core Collection Of Cucumber (Cucumis Sativas L.)

Cucumber is one of the most important vegetables in the world. At present systemic study about the genetic diversity, affinity evolutionary relations as well as the construction of core collection in cucumber are still lacking. To assess genetic diversity and population structure of this collection for future breeding, we genotyped 3318 resources with 23 high polymorphism simple sequence repeat markers.The results are as follows:(1) We selected 23 pairs of polymorphisms primer from cucumber high density genetic mapping, the 23 SSRs distribute on 7 chromosomes evenly and can amplify clear and stable bands, analysis results of population genetic diversity in 3318 resources showed high polymorphism exist in 23 SSRs, which can distinguish germplasms from different regions.(2) Three subgroups related to geographical distribution are identified, which including India and Xishuangbanna subgroup, Europe and America, Western Asia subgroup, China and East Asia subgroup. Clustering analysis were conducted by Neighbor-Joining method.(3) According to SSR analysis results, we discussed genetic evolution relationship among subgroups at the molecular level: Europe and America, Western Asia subgroup as well as China and East Asia subgroup may evolve from India and Xishuangbanna subgroup. At the same time the origin and transmission routes of cucumber have been further proved.(4) Though subgroup three(India and Xishuangbanna subgroup) own the least number of resources, both the genetic diversity and the heterozygosity are higher than subgroup one(China and East Asia subgroup) and subgroup two(Europe and America, Western Asia subgroup), which proved that cultivated cucumber originated from India. The average amplified fragment length of subgroup one and subgroup two are longer than subgroup three, proving the hypothesis that subgroup one and subgroup two evolved from subgroup three.(5) Choosing the resources that can best represent genetic diversity of germplasm resources, we construct core germplasm banks. Finally we determined 120 resources, which take up 3.6% of all the resources and can represent 80.8% genetic diversity. These findings suggest that resources from different geographical areas should be considered in breeding, and key gene related to yield can be explored by using of core germplasm resources.This study discussed the genetic structure of worldwide cucumber resources, which provided basis for further understanding of cucumber evolution, the constructed core resources can largely reflect genetic diversity of resources. The core resources can be used for resquencing and identifying of favorable genes.