Analyses Of AFLP And CpDNA Sequence For Natural Populations Of Larix Principis-rupprechtii Mayr.

Larix principis-rupprechtii Mayr. is an endemic deciduous tree species to North China, with a natural distribution range covering Shanxi Province, Hebei Province, and Inner Mongolia Autonomous Region. Besides having major economic value as a source of timber and other products, this species usually forms the dominant vegetation cover in the area it occurs, and is an important component of the entire ecosystem. With the characters of beautiful straight trunk, fast growth, strong adaptability, and effective capacity to improve soil and prevent water loss, it has been widely planted in north China now. To explore the genetic diversity, genetic evolution and genetic structure of this species, a total of 10 natural populations were analyzed using two kinds of molecular markers, i.e. AFLP and Chloroplast DNA sequence (rbcL). For AFLP analysis, based on six pairs of primers selected from 64 pairs of candidate primers, a total of 309 bands were found from the 225 individuals of the 10 populations, of which 261 were polymorphic, indicating a high percentage of polymorphic bands (84.47%). Among all the populations tested, WL population displayed the highest genetic diversity (hWL=0.273%,IWL=0.3793), while TY population had the lowest genetic diversity (hTY=0.1956, ITY=0.2798). The clustering analysis showed that these populations could be divided into 3 groups. The first was consisted of GD, WT, TY, LL, HS and XWT populations, the second was comprised of WC, FN and WYD populations, and the third included WL population only. Meanwhile, the analysis of the genetic structure revealed that these populations could also be classified into four groups, i.e., the northern, central, southern and transitional groups. The northern group was consisted of WC, FN nd YD opulations, the southern group was comprised of GD, WT, TY, L and HS populations, the central one only had WL population and the transitional group (XWT population) between southern and central groups. Mantel Test showed that there was a significant correlation between the genetic distances and the geographic distances for these populations (r=0.316, p<0.05). The analysis of AMOVA revealed a significant genetic differentiation among all the populations (Fst=0.0929, p<0.001). The same were also true for the northern group (Fst=0.0718, P<0.001) and southern group (Fst=0.0617, p<0.001). For the cpDNA marker, based on a 1318bp rbcL gene sequence, no difference was sequenced out among all the populations. Compared with the rbcL gene sequence for Larix olgensis Henry and Larix gmelinii var. japonica from the NCBI, no difference was found either. However, there were 2-3 mutations found in single nucleotides in comparison with the rbcL gene sequence for other Larch species. Nevertheless, this suggested that L. rincipis-rupprechtii Mayr. may have a closer genetic relationship with L. gmelinii. As a whole, the AFLP analysis showed that the genetic differentiation among the populations was significant, while analysis of cpDNA sequence suggested that the genetic differentiation was extremely limited among them. This indicated that the cpDNA may have much less variation than nuclear DNA. For a better understanding of the genetic evolution of this species, further work should be conducted based on nuclear gene sequence.