Abstract
Liriodendron chinense (Hemsley) Sargent is a Class II protected plant in China as natural populations are on the verge of extinction. There is still a lack of systematic research on the genetic resources of its geographic populations. In this study, we used 20 pairs of SSR markers with high polymorphism to analyze a total of 808 L. chinense samples from 22 regions, and 63 Liriodendron tulipifera Linn samples from 2 regions were used as a comparison group. The results revealed a total of 78 alleles in L. chinense, and the average expected heterozygosity (He) was 0.558, showing a low level of genetic diversity. The degree of differentiation of L. chinense was high, with the differentiation coefficient (Fst) as high as 0.302, which is related to the low gene flow (Nm = 0.578). Based on the genetic structure, principal coordinate analysis (PCoA) and phylogenetic analysis of 24 Liriodendron spp. populations, L. chinense and L. tulipifera had obvious differentiation, while the differentiation between L. chinense geographic populations was very large and irregular. Inbreeding appears within the geographic populations, and the level of genetic diversity is very low. In order to protect the genetic diversity of L. chinense, in addition to protecting the existing population as much as possible, artificial cultivation should introduce materials from multiple populations.
Highlights
The climate oscillations and topographical changes of the Late Tertiary and Quaternary have profound influences on the geographical distribution and genetic structure of species
The distribution of genetic variation at the small scale within populations and the large-scale spatial distribution among populations is one of the important characteristics of the population genetic structure. Whether it was the eastern-western subregion or the distribution pattern of “one belt and five islands”, L. chinense was clustered and distributed in the large-scale spatial, which was largely affected by the climate fluctuations since the Tertiary
The “island-like” distribution of the existing L. chinense populations resulted in mostly small populations, so the degree of inbreeding within the populations was high and the genetic isolation among the geographic populations resulted in random differentiation among the populations
Summary
The climate oscillations and topographical changes of the Late Tertiary and Quaternary have profound influences on the geographical distribution and genetic structure of species. The genus Liriodendron (Magnoliaceae), which is a relict species of the tertiary period, was widely distributed in the northern region of the Northern Hemisphere during the early to midMiocene but became extinct in Europe during the Pleistocene. There are only two sister species, Liriodendron tulipifera Linn and Liriodendron chinense (Hemsley) Sargent, of this genus [5], which are typical East Asian and North American intermittent distributions of “species pairs”. These trees are similar in shape and are famous for their rapid growth, valuable wood, and unique leaf shape, so they have important economic and ornamental value [6,7]. Due to its biological characteristics, including a small population, low seed setting rate and low seed germination rate, as well as climate change and human interference, L. chinense has become an endangered species [8]
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