Genetic diversity and population structure of the endangered species Psammosilene tunicoides revealed by DALP analysis

Psammosilene tunicoides W. C. Wu et C.Y. Wu (Caryophyllaceae) is a rare plant endemic to China. We used the direct amplification of length polymorphism (DALP) method to analyse the genetic diversity of 17 natural populations of this species from Yunnan, Sichuan and Guizhou provinces. The percentage of polymorphic bands (PPB) was 99.1% at the species level and 19.9% at the population level. The total genetic diversity (Ht) was 0.2827; the genetic diversity within populations (Hs) was 0.0594 and the coefficient of gene differentiation (Gst) was 0.7899. The results indicated low levels of genetic diversity within populations and extremely high genetic differentiation among populations. This pattern might be caused by genetic drift resulting from intensive harvesting and habitat fragmentation. It might also be a result of local adaptation. We further performed experiments on its breeding system and found a high rate of selfing in P. tunicoides, which may be partially responsible for its population structure.

Research highlights
► Psammosilene tunicoides is a famous herb in folk medicine in China. It is endangered and is the evolutionary significant unit as a monotypic genus in the family of Caryophyllaceae. So it deserves more consideration as for conservation. Southwestern China, as its main distributing area, was supposed to be the main investigation range.
► We used DALP to investigate the genetic variations among and within 17 natural populations of P. tunicoides. The result showed the low levels of genetic diversity within populations and extremely high genetic differentiation among populations.
► The genetic pattern might be caused by genetic drift resulting from intensive harvesting and habitat fragmentation. Further experiments on its breeding system found a high rate of selfing in P. tunicoides, which may be partially responsible for its population structure.
► We observed some phenotypic variations, e.g. the close stigma–anther proximity (shortest SD value) and a short time lag between the pistils becoming receptive and the pollen beginning to be shed from the stamen, which may be responsible for the high selfing rate.
► Above results indicated sustainable conversation strategies for the recovery of this species. For example, different populations should be included in ex-situ conservation plan, while manual cross-pollination should be conducted and the artificial emasculation should be employed during cross-pollination among populations.