Abstract:

Aims: Populus euphratica is a rare tree species in the extremely arid desert area of northwest China. The research on the germplasm genetic resources within the natural populations and the construction of a germplasm bank are helpful to protect the gene resources of P. euphratica.
Methods: In this study, according to the Nei’s genetic similarity among populations by using SNPs from 120 DNA fragments, the gradual clustering priority sampling method was used and t-test was performed to compare the genetic diversity within populations, the conservation units and the rest populations. A total of 58 natural P. euphratica populations from northwest China, including Xinjiang, Qinghai, Gansu, Ningxia, and Inner Mongolia, were used to obtain the different natural conservation units.
Results: The P. euphratica populations were divided into four distinct clades that demonstrated strong geographical distribution patterns (NX, SX, QH and GNM, with the GNM clade containing individuals from Gansu, Ningxia and Inner Mongolia individuals). PCA analysis confirmed the differentiation of populations, similar to population structure. Southern Xinjiang holds the major distribution of P. euphratica in China, and the higher genetic diversity than other distribution areas, and the analysis of molecular variance (AMOVA) showed that most of the variation within P. euphratica was distributed within population compared to the variation among populations. The primary core conservation units (CU3) contained three populations, and the secondary core conservation units (CU33) contained 33 populations. There may be natural ancient P. euphratica resources with putative resistance to stress in southern Xinjiang, and the average genetic diversity in southern Xinjiang was higher than that in northern Xinjiang.
Conclusion: The overall genetic diversity of P. euphratica and the number of ancient trees in southern Xinjiang were higher than those in northern Xinjiang. The priority protection of the first and second core conservation units was constructed. Combining comprehensively with habitat information, such as the severity of drought index in Xinjiang, it was recommended to increase the conservation of ancient P. euphratica trees in southern Xinjiang, and to pay more attentions to the regeneration of P. euphratica forests in northern Xinjiang.

Key words: natural population, SNPs, molecular marker, core germplasm