Genetic diversity and differentiation among populations of Bretschneidera sinensis (Bretschneideraceae), a narrowly distributed and endemic species in China, detected by inter-simple sequence repeat (ISSR)

• The genetic variability and population structure of seven Bretschneidera sinensis populations were investigated.
• There are highly significant (P < 0.001) genetic differences among the seven populations.
• There is significant correlation (r = 0.9087, P < 0.05) between genetic distance and geographic distance.
• Genetic differentiation occurred between populations from the reproductive system and recent habitat fragmentation.

Bretschneidera sinensis Hemsl., of the monogeneric family Bretschneideraceae, is an endangered species endemic in East and South China. Most of the populations are seriously threatened. Some of them are even at the brink of extinction. In this study, Inter-simple sequence repeat (ISSR) markers were used to investigate the genetic diversity within and among seven populations of B. sinensis. The results showed that Genetic diversity at species level was high (PPB: 76.7%; HE: 0.3131; H: 0.4524). However, relatively low genetic diversity existed within populations. Population in Guangdong (GD) exhibits the greatest level of variability (PPB: 65.1%; HE: 0.2573, H: 0.3766), whereas the population in Fengyangshan (FYS) finds its own variability at the lowest level (PPB: 51.5%; HE: 0.1959, H: 0.2886). Based on the genetic analyses of the ISSRs, a relatively high level of genetic differentiation among populations was revealed by Nei's gene diversity statistics (22.3%), Shannon's information measure (21.5%) and analysis of molecular variance (AMOVA) (18.4%). The main factors responsible for the relatively high level of differentiation among populations are probably related to the predominant outcrossing reproductive system and recent habitat fragmentation, and a significant correlation was found between genetic distance and geographic distance (r = 0.9087, P < 0.05). The high diversity found in this study holds promise for conservation and restoration efforts to save the endangered species from extinction.