| Actinidia chinensis and A. chinensis var. deliciosa belongs to A. chinensis complex with a wide distribution range along centre, southeast and southwest China. The fact that high-quality kiwifruit cultivars are mostly selected from wild population of A. chinensis complex makes this taxon be of great economic value. A wide-range investigation and research of natural kiwifruit population facilitates our exploring of their ploidy variation and the distribution pattern of different variants and ploidy races, contributes our selection of high-quality phenotype and genotype, and instruct the decision of ploidy breeding strategy. At the same time, the study of variation in genetic and geographic distribution and the primary discussion on phylogeography based on chloroplast DNA haplotype would provide important insight into the distribution pattern of the genetic variation, the historical evolution process, and the issues concerning hybridization pattern and gene flow guided by pollen in Actinidia chinensis complex. The results might provide scientific basis and theoretical guidance for the development of wise conservation strategy and the selection of new cultivars with superior-characters. Then rational utilization of kiwifruit natural resource and sustainable development of kiwifruit industry will be fulfilled.The main results were as followed:(1) We detected the ploidy level of 43 natural populations of A. chinensis and var. deliciosa from Guizhou, Hunan, Guangxi, and Guangdong province using flow cytometry. Both variants contained various ploidy races including diploid, tetraploid, hexaploid, and octoploid. The hexaploid and octoploid A. chinensis, and diploid var. deliciosa were detected for the very first time. Moreover, we firstly found the triploid in kiwifruit. The statistical analysis on diploid, tetraploid, and hexaploid data revealed the trend of adding ploidy level with increasing altitude and latitude, and decreasing longitude. From the distribution pattern, we found the rule that A. chinensis distributed to the east, whereas var. deliciosa to the west. And we also discovered a gradual transition from diploid to hexaploid across the latitudinal and longitudinal gradient, that is, the frequency of polyploidy increased from east to west, south to north.(2) 17 haplotypes were identified within cpDNA fragments of samples from 26 A. chinensis populations and 28 var. deliciosa populations. There were many A. chinensis or var. deliciosa-specific haplotypes and rare haplotypes. And the haplotypes were regionally distributed, common haplotype located in central and west of China, whereas rare halotypes occurred in eastern China. The total genetic diversity of A. chinensis complex based on cpDNA sequences was relatively high (hT= 0.7640), whereas within-population diversity was low (mean value=0.4184). The haplotype diversity and nucleotide diversity of A. chinensis (0.7340 and 0.0018, respectively) were much higher than that of var. deliciosa (0.6162 and 0.0004, respectively). The mean value of pairwise Fst between A. chinensis and var. deliciosa populations (0.5764) was larger than that among A. chinensis populations (0.4952), or that among var. deliciosa populations (0.1519); AMOVA results also indicated that the differential between two variants was high which might caused by their geographic isolation. The fact that genetic differentiation coefficients of the whole populations were low (Nst=0.433, Gst=0.460, Fst=0.428) demonstrated frequent paternal gene flow mediated by pollen. Haplotype H2 and H3, locating in the interior nodes of the haplotype network with high frequency were inferred to be ancient haplotype. They distributed in Yugui Plateau, Willing Mountain, and Xuefeng Mountain, which happened to be of high genetic diversity, indicating that these areas might serve as glacial refugia. The existence of ancient range expansion event couldn’t be supported by neutral testing. |
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