In this study, 13 microsatellite loci were analyzed to reveal the genetic diversity and population structure of A. albus from 24 populations in Sichuan, Yunnan, Hubei Province and they all expressed high polymorphism with an average PPL of 95.19%. According to the results, we observed a moderate genetic diversity of this species (He = 0.504, I = 0.912). In comparison, the genetic diversity observed was lower than in other studied Amorphophallus species using microsatellite markers, e.g., in A. paeoniifolius (He = 0.598, I = 1.172) , but higher than the estimated mean of genetic diversity of endemic species (He = 0.42) summarized by Nybom . Genetic diversity of plant species usually depends on their breeding system, distribution or life form [33–34]. Generally, perennial species with wide distribution, self-incompatible mating system and seed dispersal by animals possess higher genetic diversity . For A. albus, which is a perennial herb with limited distribution showing self-incompatible mating system and endozoochory, it is supposed to have relatively higher genetic diversity. However, as an important economic crop, A. albus was inevitably disturbed by human activities such as habitat destruction and over excavation in recent years similar to A. konjac . Consequently, wild populations of A. albus can hardly be found in nature. Moreover, most farmers, who cultivated this species for commercial purposes, tend to use asexual reproduction to get more corms and shorter life cycles . This finally led to a reduced genetic diversity which is clearly observable in the populations of SDC and JLC. In contrast, some cultivated populations still maintain high genetic diversity, even higher than those wild populations, like HLX and LIZ. Presumably, these populations were transplanted from their native habitats and cultivated without or just little human disturbances. Wild populations comprises of not more than 50 individuals may lose genetic diversity in bottleneck events. Another possible reason is, that the existed wild populations were feral from cultivated populations and did not possess much genetic variation originally. According to our results, the populations with high genetic diversity are almost in or around Jinyang County, whilst the populations with the lowest genetic diversity are present in Pingshan and Suijiang. Based on our results, we assume that Jinyang is the natural origin of A. albus, and the gene flow from Jingyang to Pingshan showed a trend of expanding towards east along the river. This pattern could also be observed from other species native to the dry and hot valleys along the Jinsha River [37–38].
The genetic analysis of A. albus indicated a high level of differentiation (Fst = 0.29) and low gene flow (Nm = 0.61) among populations. According to Wright , populations show high genetic differentiation and low gene flow when Fst > 0.25/Nm < 1. High genetic differentiation may result from heterogeneous environments . Though all the populations distributed along Jinsha River, much differences in temperature, humidity, vegetation form existed between the hot-dry valleys and warm-dry valleys . Additionally, Araceae species commonly pollinated by small insects such as ants, beetles and hover flies [42–43], and A. albus is pollinated by rove beetles (Tang et al., unpublished data). This small insect pollination mating system and the complex geography may have limited gene flow among populations and therefore promoted genetic differentiation of this species . Moreover, though the fruits of A. albus possess traits for seed dispersal by birds, but this could not be observed.
The observed fixation coefficient (Fis) in most loci were less than zero (Table 3) which indicates a great excess of heterozygosity in this species. This is a common phenomenon resulting from the applied sampling strategy, asexual reproduction, heterosis and too small breeding populations [45–47]. Regarding A. albus, sampling may be one of the reasons because quite a number of sampled populations belonged to small populations of less than 50 individuals. Another important reason is asexual reproduction independent whether the plants are cultivated or in growing the wild. During cultivation, the farmers usually cut inflorescences in order to get bigger tubers, because asexual reproduction allows to harvest commercial konjak faster . In latter case, there are always many ramets around an adult plant, which also could be observed from the related species A. paeoniifolius . As a result, asexual reproduction seems to be the main reason for excess of heterozygosity in A. albus.
In this study, the results of UPGMA cluster tree, Bayesian cluster analysis and Mantel test indicated that the genetic distance was slightly positive correlated with the geographical distance, and geographically close populations are usually clustered together (Fig. 1–2). These results showed that most of the cultivated populations nowadays are collected from native populations. But some populations were put in different places between the two clusters analysis like MYZ. Those populations mostly are the important base of their county of A. albus cultivation, every year people buy corms from other counties to increase their own variety. On account of different algorithms of the two software, these populations may be treated differently. Thus, reintroduction was proved to exist in many populations. In addition, the occurrence of three ex-situ cultivated populations in cluster I together with populations of MYZ, BJ and SYC indicated an introduction of these populations either from Yongshan, Leibo or Pingshan County. Reintroduction of plants from MYZ in downstream areas is also conceivable. The occurrence of population SDC in cluster IV (Fig. 2) is may be caused by introgression after hybridization with A. konjac. Spatial proximity to the distribution area of the latter species together with the already proved cross-breeding of both species  support this assumption.