Abstract
AimsBoth Rheum palmatum and R. tanguticum are important but endangered medicinal plants endemic to China. In this study, we aimed to (i) investigate the level and pattern of genetic variability within/among populations of those species; (ii) evaluate genetic differentiation between both species and its relationships and ascertain whether both species are consistent with their current taxonomical treatment as separate species; and (iii) discuss the implications for the effective conservation of two species.MethodsTotal 574 individuals from 30 populations of R. palmatum and R. tanguticum were collected, covering the entire distribution range of two species in China. The genetic variation within and among 30 populations was evaluated using inter-simple sequence repeat (ISSR) markers.Important FindingsTwelve selected ISSR primers generated a total of 175 fragments, 173 (98.86%) of which were polymorphic. The Nei's gene diversity (H) and Shannon's index (I) of both species were high at species level (H = 0.3107, I = 0.4677 for R. palmatum; H = 0.2848, I = 0.4333 for R. tanguticum). But for both species, the genetic diversity was low at population level, and average within-population diversity of R. palmatum was H = 0.1438, I = 0.2151, and that of R. tanguticum was H = 0.1415, I = 0.2126. The hierarchical AMOVA revealed high levels of among-population genetic differentiation in both species, in line with the gene differentiation coefficient and the limited among-population gene flow (R. palmatum: Φst = 0.592, Gst = 0.537, Nm = 0.432; R. tanguticum: Φst = 0.567, Gst = 0.497, Nm = 0.507). By contrast, only 6.52% of the total genetic variance was partitioned between R. palmatum and R. tanguticum. Bayesian analysis, UPGMA cluster analysis, and PCoA analysis all demonstrated the similar results. A significant isolation-by-distance pattern was revealed in R. palmatum (r = 0.547, P = 0.010), but not in R. tanguticum (r = 0.241, P = 0.100). Based on these results, effective conservation strategies were proposed for these two species. The small molecular variance between R. palmatum and R. tanguticum revealed that they had a common ancestor, and we considered that these two species might not be good species.
Highlights
Preserving genetic diversity of species is one of the primary goals of conservation planning, because long-term survival and evolution of species depend on the maintenance of sufficient genetic variability within and/or among populations to accommodate new selection pressures brought about by environmental changes [1]
Most of fragments were shared across species, and only 5 and 3 bands were unique to R. palmatum and R. tanguticum, respectively
Our results showed that genetic diversities were pretty low at population level (R. palmatum: polymorphic bands (PPB) = 41.42%, H = 0.1438, I = 0.2151; R. tanguticum: PPB = 41.90%, H = 0.1415, I = 0.2126), and relatively higher at species level (R. palmatum: PPB = 98.29%, H = 0.3107, I = 0.4677; R. tanguticum: PPB = 91.43%, H = 0.2848, I = 0.4333), which is similar to the level of genetic diversity reported by Hu et al on P. tanguticum (PPB = 92.94%, H = 0.2689 I = 0.4163) [6]
Summary
Preserving genetic diversity of species is one of the primary goals of conservation planning, because long-term survival and evolution of species depend on the maintenance of sufficient genetic variability within and/or among populations to accommodate new selection pressures brought about by environmental changes [1]. (Polygonaceae) is endemic to China, and comprises four described species R. laciniatum Prain) [3] The former three ones are the original plants of official rhubarb which is a widely used and one of the very famous traditional Chinese medicines as a purgative and anti-inflammatory agent [4]. R. officinale and R. palmatum face great pressure exacerbated by the reduction of the wild resources of R. tanguticum, and both are treated as ‘‘threatened’’ species in China. The genetic information of R. tanguticum was neither been really estimated nor sufficient for the conservation of the endangered but valuable species, and the genetic information for R. palmatum remains unknown
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