Phylogeography of cultivated and wild ophiopogon japonicus based on chloroplast DNA: exploration of the origin and sustainable cultivation

Abstract

Background: Ophiopogon japonicus, mainly planted in Sichuan (CMD) and Zhejiang (ZMD) province in China, has a lengthy cultivation history. During the long period of domestication, the genetic diversity of cultivated O. japonicus has substantially declined, which will affect the population continuity and evolutionary potential of this species. Therefore, it is necessary to clarify the phylogeography of cultivated O. japonicus to establish a theoretical basis for the utilization and conservation of the genetic resources of O. japonicus.

Result: The genetic diversity and population structure of 266 O. japonicus individual plants from 23 sampling sites were analyzed based on 4 chloroplast DNA sequences (atpB-rbcL, rpl16, psbA-trnH and rpl20-5'rps12) to identify the effects of domestication on genetic diversity of cultivars and determine their geographic origins. The results showed that cultivated O. japonicus and wild O. japonicus had 4 and 15 haplotypes respectively. The genetic diversity of two cultivars (H_d = 0.35700, π = 0.06667) was much lower than that of the wild populations (H_d = 0.76200, π = 0.20378), and the level of genetic diversity in CMD (H_d = 0.01900, π = 0.00125) was lower than that in ZMD (H_d = 0.06900, π = 0.01096). There was significant difference in genetic differentiation between the cultivated and the wild (F_ST = 0.82044), especially between the two cultivars (F_ST = 0.98254). This species showed a pronounced phylogeographical structure (N_ST > G_ST, P < 0.05). The phylogenetic tree showed that the genetic difference between CMD and ZMD was not enough to distinguish the cultivars between the two producing areas by using O. amblyphyllus Wang et Dai as an outgroup. In addition, both CMD and ZMD have a closer relationship with wild populations in Sichuan than that in Zhejiang. The results of the TCS network and species distribution model suggested that the wild population TQ located in Sichuan province could serve as the ancestor of cultivated O. japonicus, which was supported by RASP analysis.

Conclusion: These results suggest that cultivated O. japonicus has experienced dramatic loss of genetic diversity under anthropogenic influence. The genetic differentiation between CMD and ZMD is likely to be influenced by founder effect and strong artificial selection for plant traits. It appears that wild populations in Sichuan area are involved in the origin of not only CMD but also ZMD. In addition, we also raise some suggestions for planning scientific strategies for resource conservation of O. japonicus based on its genetic diversity and population structure.

Keywords: Conservation; Domestication; Ophiopogon japonicus; Origin; Phylogeography.