Analysis of genetic diversity of ancient Ginkgo populations using SSR markers

Ginkgo biloba L., a famous relict plant, is the only surviving species of Ginkgopsida. To explore the genetic variation of geographic populations and possible refuges of Ginkgo during the glacial period, 216 samples from 6 ancient populations and 2 cultivated populations were analyzed using 22 simple sequence repeat (SSR) markers. A total of 231 alleles were detected at the 22 SSR loci, and the average expected heterozygosity (He) was 0.808, indicating a high level of genetic diversity. The STRUCTURE, phylogenetic tree and principal coordinate analysis (PCoA) results showed that the 8 populations could be divided into 2 groups, namely, the eastern group (TM, NJ and PZ) and southwestern group (PX, DY, MJ, FG and WC). The eastern and southwestern groups had 15 and 14 unique alleles, respectively. Among the populations, population TM from the east had the highest genetic diversity and allelic richness, and 9 rare alleles and 8 unique alleles were detected in this population. Although the genetic diversity of population WC from the southwest was lower than that of population TM, 8 rare alleles and 2 unique alleles were detected in WC. It was speculated that the areas of population TM in the east and population WC in the southwest were refuges during the glacial period. In addition, a total of 7 unique alleles were detected in the 2 cultivated populations from the east, suggesting that there may have been other refuge areas during the glacial period.