EST-SSR marker-based investigation on genetic diversity and genetic structure of Juglans mandshurica Maxim. in Shandong Province of China

Juglans plant with important ecological and economic value is endangered in China, and the basis for its protection is the genetic diversity assessment. In the present study, the genetic diversity and the genetic structure of 134 samples from nine J. mandshurica populations with two related species were surveyed by EST-SSR markers. The results showed that 77 alleles were amplified within nine EST-SSR markers which had high polymorphism (PIC = 0.507). Compared with other Juglans species in China, the genetic diversity of J. mandshurica population in Shandong areas was relatively low (HO = 0.333, I = 0.705). The AMOVA analysis showed that 89% variation occurred within the population of J. mandshurica in Shandong areas while 11% occurred inter-populations. The low genetic differentiation (FST = 0.103) and the high gene flow (Nm = 2.894) among populations may be related to the long-distance transmission of pollen. The results of Mantel test showed that there was no significant correlation between geographic distance and genetic distance. UPGMA cluster analysis divided eight J. mandshurica populations in Shandong areas into two groups. The results of STRUCTURE analysis suggested interspecific introgression exists between J. mandshurica and common walnuts (J. regia L.). These genetic data would be great significance for biodiversity conservation for endangered J. mandshurica.