| Chinese Cherry generally refers to species Prunus pseudocerasus Lindl.(Cerasus pseudocerasus Lindl.), belong to Rosaceae, subfamily Prunoideae, genera Cerasus, which can be mainly devided into three groups:the cultivated varieties, local populations and wild populations.The local and wild populations, which contains the rich Chinese Cherry germplasm, have the widest geographic distribution and are the most recently diverged population within the species C.pseudocerasus. Due to the closest affinity of the cultivated varieties, they also serve as an important gene source for genetic improvement of the Chinese Cherry cultivated varieties. However, many questions regarding the genetic diversity, population structure and molecular phylogeographic of these populations are still unanswered due to the similar morphology and limited overlapping of the sampling. In this study, we evaluated the genetic diversity and population genetic structure using intergenic spacer sequences of chloroplasts. At the same time, we investigated the origin of Chinese Cherry as well as the genetic relationship between wild and local populations based on the population structure and phylogeographic analysis. We summarized some results as following:1. Chloroplasts sequence genetic diversity of Chinese CherrySampled200Chinese cherry individuals, collected from17populations, i.e.7local populations and10wild populations. The genetic diversity of all17populations, both the wild and local populations, was respectively evaluated with the chloroplasts intergenic spacer trnL-rps16sequences. The results show that:1) the genetic diversity of all poulations was in lower level, all17populations were defining15chloroplasts haplotypes, the range of haplotype diversity (h) were distributed from0.000to0.718, while, nucleotide diversity varied from,0.00000to0.00344, with an average of0.0018.2) comparing with local population, high levels of genetic diversity were observed in wild population, the haplotype diversity (h) and nucleotide diversity (π) of wild group were0.565and0.0021, respectively, and for local population were0.152and0.0006, is the3to 4times of local population. This study detected lower level genetic diversity compared with previous results based on fingerprint marks. This may associate with the characteristics of chloroplasts sequence itself. Since the haploid genomes makes maternally inherited organelle markers and the effective population size for the chloroplast genome is half of that of the nuclear genome, so, The influences of demographic bottleneck would be stronger on plastid than on nuclear markers, the levels of genetic diversity would be lower in organelle markers.2Population genetic structure and phylogeographic patternThe population genetic structure and phylogeographic of Chinese Cherry were analysed based on the above chloroplasts DNA sequence. The result indicated that:1) The genetic differentiation are not significant (P>0.05) among all populations, except for WSN and WQC based on pairwise Fst. AMOVA reveal the main genetic variation73.72%(FST=0.26276, P=0.0000) within the populations and17.97%(FSC=0.19595, P=0.0000) among populations. While, only8.31%(FCT=0.0831, P=0.13783) variation between wild and local populations.2) Three haplotype clusters (Ⅰ-Ⅲ) were identified in the Neighbor-Joining (NJ) tree based on15haplotypes. But these clades did not associated with both the geographic distribution and and population division. Median-joining network showed Hapl was nested and widespread in all populations. While, the haplotype Hap3as the interior node was mostly restricted to wild populations.3) The genetic distance among all of the17populations are in low level from0.00000to0.00337based on Jukes-Cantor model. Neighbor-Joining genetic distance clustering shows that WSN, WQC and WTL from wild populations together as a subclade, the others cluster another.4) Population structure, based on the frequency and degree of haplotype divergence across all populations, were0.209and0.253, for GST and NST, respectively. In local population were0.016and0.020, wild population were0.2and0.249, respectively. This result indicated that genealogical structure was slightly present, but not significant.5) Negative and insignificantly value in the Tajima’s D and Fu and Li’s D*and F*, except for local population, the Tajima’s D value was significantly negative (Tajima’s D=-1.73683; P<0.05). It closely fitted the distributions of the sudden expansion model. This was further confirmed by the unimodal mismatch distributions. All of the above result indicate low levels of grenetic differentiation and widely genetic flow in Chinese Cherry. This may associated with inbreeding mating system and the high capabilities of animal-ingested seed dispersal system in Chinese Cherry itself. In addition, the low evolutionary rates of plastid DNA and the short time of isolation since the last glacial retreat is seemingly not long enough for differentiating these populations among distribution range. |
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