1. Introduction
Yam
is considered the common name for plants, with over 600 species ofDioscorea genus. The species of yams widely cultivated in the
world are D. bulbifera , D. panthaica , D. esculenta ,D. japonica , D. trifida , D. pentaphylla , andD. rotundata (Lebot, 2009). Yams are also one of the 10 most
important edible tuber and root plants in the world and next to potato,
cassava, and sweet potato in yield (Shewry, 2003). They
play an important role in sustaining many livelihoods in the tropics and
subtropics (Tschannen et al., 2005; Wu et al., 2019). In China, yam is
known as a medicinal and edible crop with high nutritional and medicinal
value; its tuber is rich in starch, protein, and medicinal ingredients
(e.g., allinogenin, diosgenin, and dehydroepiandrosterone; Lebot, et
al., 2019).
In China, yam resources are extremely rich, with a total of 93 species.D. opposita , D. alata ,D. persimilis , D. fordii , and D. quinquelaba are
widely cultivated in China nowadays (Huang, 2011). Yams are cultivated
in other provinces, except Qinghai and Tibet, including a large number
of local varieties. However, they have long been regarded as “orphan”
or “neglected” crops despite their considerable edible and medicinal
value and received little attention or investment from researchers
(Tamiru et al. , 2017).
Moreover,Dioscorea is mainly dioecious, rarely flowering, and has
difficult forming mature seeds
(Bressan et al. , 2011). The
development of
medicinal
ingredients from a few species of yam has long been emphasized in China
(Li et al., 2018; Lebot et al., 2018; Cheng et al., 2020), but the
analysis of the resource types and genetic diversity of yam is
insufficient. Moreover, several studies only focused on D. alata ,
and the method of resource evaluation is relatively simple (Siqueira et
al., 2014; Arnau et al., 2017; Wu et
al., 2019). In the long-term cultivation and domestication process, the
variation types of yam are complex, and a single classification method
is difficult to identify, thereby causing confusion in various records
and nomenclatures and even in the classification of some species. These
factors seriously hinder the resource conservation and further
utilization of yam.
Therefore, studying the genetic diversity, genetic variation, and
population structure of yam is considerably important to its origin,
distribution, resource utilization, parental selection, and development
(Mignouna et al., 2003). So far, phenotypic traits, isozyme, karyotype
analysis and DNA diversity have been used to describe the genetic
diversity of germplasm (Sartie et al., 2012; Nemorin et al. ,
2013; Kouam et al., 2018; Ghorbani
et al., 2020; Cao et al., 2020).
However, research on the genetic diversity of yams has focused on a few
species in Africa and the Americas.
Anokye et al. (2014) used
morphological descriptors to dissect the phenotypic diversity ofD. alata from Ghana and Nigeria and divided these materials into
different clusters independent of geographic origin. Mignouna et al.
(2002) evaluated the genetic variation of 45 cultivated yams (D .cayenensis /D. rotundata complex) from Cameroon by using
morphology and isozyme, and the clustering results of the two were
relatively consistent. Silva et al. (2016) used 12 microsatellites and
four morphological markers to analyze the genetic diversity and
structure of 89 yam (D . alata ) in Brazil; a high diversity
is found in Brazilian yam, but it is not related to geographical
location. At present, despite some reports available on the genetic
diversity of Chinese yam local varieties, the research methods were too
single, the number of molecular markers was small, and the
representation of germplasm source regions was poor.
In the present study, large-scale yam resources were collected in 21
provinces, including the main species used in cultivation to fully
identify and evaluate the genetic information of yams in China. The
genetic diversity, genetic relationship, and population structure of
yams were evaluated using the combination analysis of phenotypic traits
and two molecular markers (SRAP and SSR). The results could provide a
basis for yam classification, breeding, germplasm innovation,
utilization, and variety protection.