Nuclear genetic diversity and population structure of a vulnerable and endemic orchid (Cymbidium tortisepalum) in Northwestern Yunnan, China

- 404 accessions from 28 locations across its major distribution range were used to assess the genetic diversity and population structure of C. tortisepalum by 13 nSSRs markers.
- No significant LD was found. A high degree of genetic diversity and low genetic differentiation among natural populations were detected.
- Structure, NJ tree and UPGMA tree cluster analysis divided 28 populations into two major groups. Two MUs for conservation concerns should be taken.

Cymbidium tortisepalum Fukuy., an economically important perennial herbaceous plant, is of high ornamental value owing to its flower shape, foliage, and fragrance. Unfortunately, it is under threat of extinction due to excessive collection for commercial purposes and habitat loss. It has been listed as a vulnerable species in China. Here, 404 accessions from 28 locations across its major distribution range were used to assess the genetic diversity and population structure of C. tortisepalum by analyzing 13 nuclear simple sequence repeats (nSSR) markers. Overall, 199 alleles were detected that ranged in number per locus from 6 (SSR9) to 26 (SSR10), with an average of 15.31 alleles per locus. No significant linkage disequilibrium (P > 0.05) was found. A high degree of genetic diversity was observed in this species. Low genetic differentiation among the 28 natural populations was detected, which might have been caused by high gene flow. Analysis of molecular variance revealed 89.25% molecular variation within populations. The high level of genetic diversity and low genetic differentiation implied that the fragmented habitat and isolated populations of C. tortisepalum might be due to recent overexploitation. Consistent with the results of Structure analysis, the neighbor-joining tree and unweighted pair group method of averages cluster analysis divided the 28 natural populations into two major groups, which should be taken as two management units for conservation purposes. These genetic data provide the first understanding of the population genetic structure of C. tortisepalum in its major distribution range, and will be helpful for developing measures to conserve this vulnerable and endemic species.