Medicinal plants have been used as important sources of medicine to prevent and treat many human diseases in traditional cultures all over the world for thousands of years[1–2]. However, given the dramatically increasing demand for plant-derived medicine, many medicinal plants are under overexploitation, increasing their risk of extinction in the wild[3–4]. Generally, wild resource contains great genetic variations and beneficial genes before domestication and artificial selection, providing a reservoir of genetic variation for exploiting in breeding efforts[2]. Therefore, effective measures for the conservation need to be taken to further protect the wild resources of medicinal plants. Genetic diversity underlies adaptation and evolution of plants, which allows for dealing with various biotic and abiotic stresses in changing environments [5–6]. It is also the basis of the plasticity of secondary metabolism, and thus the production of medicinal compounds[7–8]. Therefore, investigating the genetic variation of medicinal plants in the wild is vital to plan conservation strategies for preserving medicinal plants, as well as breeding programs[9–10].
Plant domestication is an episode in which human-mediated selection favors phenotypes characterizing plants from wild resources, mainly through artificial selection[11–12]. Domestication of plants not only modifies their phenotypes but also has major impacts on the genetic variation [13–15]. One common genetic effect of domestication is the decrease of genetic diversity compared to their wild resources[16]. The loss of genetic diversity may lead to the reduction of the ability to long-term survival and evolution in changeable environments[17–18]. It is reported that the extent of the loss of genetic diversity may differ considerably among domesticated plants due to various life-history traits and evolutionary history [19]. For example, about one-third of genetic diversity was lost in soybean[20]and maize[21]compared to their wild relatives, while a majority of genetic diversity was lost in wheat[22]. The difference in extent of the loss of variation lies on the initial population size and the duration of that period[13]. Thus, knowledge of how domestication affects genetic diversity and structure across the range of both wild and cultivated populations is critical for the management and improvement of cultivars of medicinal plants in the future[15, 23]. Up to date, most studies on effect of domestication on genetic diversity have focused on agronomic crop[12–14, 19, 24], with less attention being paid to medicinal crops. Although a small number of all known medicinal plants have been studied on their population genetics, e. g. Scrophularia ningpoensis[8], Atractylodes macrocephala[25] and Cannabis species[24], numerous ongoing domestication processes have yet to be studied, and these has been of interest to medicinal plant genetic resources conservation and breeding programs.
Angelica dahurica (Hoffm.) Benth. et Hook. f. ex Franch. & Sav., is a perennial herb belonging to the genus Angelica of the family Apiaceae, mainly distributed in North and Northeast China, Japan, Korea, Russia (Siberia)[26]. Dichogamy has been detected in A. dahurica, which is an effective mechanism to encourage outcrossing and avoid selfing[27]. The pollination mechanisms of the Umbelliferae plants are always thought to be wind or insect pollination[28]. Such mechanisms have been observed in the Angelica species, such as A. biserrata[29]. Therefore, the mating system of A. dahurica is considered to be outcrossing. The dry root of the species, named as “bai zhi” (Angelicae Dahuricae Radix), is a famous traditional Chinese medicine, which has been used as a food additive as well as a folk medicinal therapy of headache, rhinitis, cold and toothache amongst others in East Asian countries (Korea, China, and Japan) for thousands of years[30–32]. A. dahurica cv. ‘Hangbaizhi’ and A. dahurica cv. ‘Qibaizhi’, two cultivars of A. dahurica, are widely cultivated in China, which have gone through evolution by artificial selection for more than 1000 and 200-400 years, respectively[26, 30, 33]. Long term artificial selection has led to great changes in the root phenotypes of the two cultivars compared with their wild species, and also decreased the adaptability (disease and insect resistances) to environment[26, 34]. Herein, we supposed that the cultivated A. dahurica (the two cultivars) may lose some genetic diversity and highly differentiate from this wild species during the domestication process in the past decades. However, so far, few studies have concerned on how domestication affects the genetic variation of cultivars of A. dahurica. There is still lack of studies on genetic diversity and population structure of A. dahurica and it culitvars.
In previous study, we had developed highly polymorphic SSR markers by transcriptome sequencing for A. dahurica[35], providing efficient molecular markers to conduct the population genetics on A. dahurica. In this study, we aim to: (1) access the levels of genetic variation and differentiation within and between wild A. dahurica and its cultivars; (2) clarify how the domestication process influence on genetic variation of this species. Hopefully, the outcomes of this study could provide valuable information for genetic resource conservation and breeding programs of A. dahurica.