Abstract:

Objective: SSR markers were employed for an analysis of population structure of a collection of germplasm resources of Populus deltoides,and a core collection of the germplasm resources was constructed in order to provide a theoretical basis for scientific management,efficient utilization and effective protection of germplasm resources of the species. Method: The genetic structure of 338 individual trees of P. deltoides collected at 23 sampling sites of 6 provenances were analyzed using 15 pairs of SSR primers. Genetic diversity parameters such as number of alleles (N_a),effective number of alleles (N_e),Shannon's information index (I),observed heterozygosity (H_o),Nei's diversity index (H),polymorphic information content (PIC) were calculated by GeneAlEx 6.503 and other software. And the principal coordinates (PCoA) analysis was also carried out. The core collection was constructed by using the method of grouping and stepwise clustering,combining with the method of maximizing the number of alleles and the sampling strategy of rare allele priority. More individuals were added in the core collection to capture 100.00% of the alleles forming an optimized core collection. The validity of the core collection and the optimized core collection was verified by t-test and PCoA analysis. Result: The population structure showed that six provenances were divided into three types:the individuals originated from St. Lawrence River Basin (Que) and Columbia River Basin (Was) were classified as one group,while those from the middle and lower Mississippi River Basin (Mis,Lou,Ten) were classified as another group,and those of the Iow provenance from the upper Mississippi River were into one group. Based on the population structure,19 core germplasms were screened,accounting for 5.62% of the original collection,the retention rates of N_a,N_e,I,H_o,H,PIC were 79.83%,102.75%,103.39%,125.31%,104.72% and 105.27%,respectively. t-test and PCoA analysis showed that the core collection was representative. By adding 15 individuals with missing alleles to the core collection,the optimized core collection including 34 individuals was constructed,and the sampling ratio was 10.06%. The retention rates of N_a,N_e,I,H_o,H,PIC were 100.00%,107.94%,110.93%,119.48%,107.52% and 109.19%,respectively. The results of t-test and PCoA analysis showed that there was no significant difference between the genetic diversity of the optimized core collection and the original collection,and the genetic information of the response was better than that of the core collection. Conclusion: The six provenances of P. deltoides resources were divided into three types:North-type (Que,Was),Middle-type (Iow) and South-type (Lou,Ten,Mis). There was no significant difference between the genetic diversity of the core collection and the optimized core collection constructed by multiple strategies and the original collection,which could well represent the genetic diversity of the resource population of P. deltoides. On the basis of preserving genetic diversity information of the original collection,the optimized core collection could remove the genetic redundancy. The results were beneficial to the effective protection and scientific utilization of P. deltoides resources and laid a solid foundation for poplar breeding.

Key words: Populus deltoides, population structure, core collection