Genetic diversity and evolutionary history analysis of natural populations of Juniperus sabina L.

To conserve the natural germplasm resources of Juniperus sabina L. reasonably and effectively, the historical origin of the distribution pattern was traced and explained. In this paper, ribosomal DNA internal transcribed spacer (ITS) sequences of 388 individuals from 10 natural J. sabina populations in the Inner Mongolia Autonomous Region, Shaanxi, Gansu, and Qinghai Province of China were sequenced and analyzed. Results showed that the total length of the ITS sequence was 1089 bp, which contained 25 mutation sites and defined 32 haplotypes, including shared haplotypes H4 and H6. Based on molecular variation analysis (AMOVA), J. sabina exhibited mainly within-population variation, accounting for 95.04%, with only 4.96% of variation among populations. Differences between populations were significant (F_ST=0.0496, P<0.001). Haplotype network analysis showed that H4 and H6 were ancient haplotypes, from which other haplotypes were derived. The genetic differentiation coefficient N_ST (0.072) was less than G_ST (0.105), indicating that there was no obvious pedigree geographic structure in the J. sabina populations, and they had not experienced a significant expansion process in history. The maximum parsimony (MP) tree showed all haplotypes were divided into two clusters. Mantel test indicated that there was no significant correlation between genetic distance and geographic distance (R²=0.0649，P>0.05). It is speculated that J. sabina originated about 12.38 Mya in the Middle Miocene of the Tertiary, with possibly many small refuges of J. sabina in the Quaternary glacial period. Sand burial, which has a better ability to produce adventitious roots, and sexual regeneration environments may be the decisive factors for the higher genetic diversity of sandy land populations than that of mountain populations.