Genetic diversity and core collection extraction of Robinia pseudoacacia L. germplasm resources based on phenotype, physiology, and genotyping markers

Robinia pseudoacacia L. (black locust) is a multipurpose tree species for conservation ecology, feeding and forestry industry in China. In the present study, 13 phenotypic, 3 physiological characters and 48 microsatellite markers (37 Expressed Sequence Tag microsatellites and 11 genomic SSRs) were used for genotyping the 1054 black locust trees from ex-situ collections to assess the diversity and extract a core germplasm collection. The original breeding population of Robinia pseudoacacia L. showed distinct phenotypic and physiological differences for most traits under investigation; the 15 traits (93.75%) had a coefficient of variation greater than 10% for all assessed indicators, showed the abundant phenotypic diversity. Similarly, high genetic diversity was estimated in the raw population, with an average number of different alleles (Na), Shannon's Information Index (I), gene diversity (H), and the polymorphic information content (PIC) of 9.455, 1.357, 0.654 and 0.624 per locus, respectively. Four sub-populations were identified with weak genetic structures. Three hundred thirty-two individuals (deleted 8 duplicate individuals with two types of data) were extracted from the original population, including a core collection of phenotypic traits (24 individuals), physiological traits (14 individuals) and molecular markers (308 individuals). This was 32.07% of the 1054 trees of the original breeding population and covered seven collection forest bases. Subsequently, the study compared the genetic diversity parameters, coincidence rate of range, principal component analysis, and frequency distribution test traits for the original and core populations. No significant difference was found between them, which indicated that the core germplasm population could well represent the original population. This study provides valuable information for Robinia pseudoacacia L. germplasm management, and its established core collection may be used in future studies of genome association and breeding programs.