The Classification And Evolution Study Of Species In Subgenus Ceratotropis Collected In China

Subgenus Ceratotropis is one of the important subgenera in genus Vigna in Leguminosa, which can be divided into three sections ( section Angulares, Ceratotropis and Aconitifoliae) consisting of 21 species. It mainly distibutes in Asia, including several important food legume cultigens such as mungbean, adzuki bean, rice bean and so on. China is rich in species of subgenus Ceratotropis and is recognized as one of the origins and diversity centers of mungbean and adzuki bean. Therefore it is of great importance to collect and study the the species in subgenus Ceratotropis for breeding purpose and biodiversity conservation. However, compared with Japan, India, Thailand and several other Asian countries the study of these species is left behind. Thus in this research we studied a total of 96 accessions including 63 representive samples collected in China and 33 mainly from other countries as reference species. Based on 17 morphological traits, 57 pairs of adzuki bean SSR primers and ITS sequence-secondary structure variation, the relationships of inter-sections, inter-species and intra-species are explored. Meanwhile, the evolution rates of different species and sections are compared. The potential genome donors of one polyploid sepecies are also discussed. The main results of all above analysis showed as follows:1. The analysis of 96 accessions in terms of distinct morphological traits indicates section Angularis and section Ceratotropis are distinctly related among the two groups which have been separated by morphological traits. Among the three sections section Aconitifoliae is most distinctive for it is characterized by common traits of the rest two sections. In section Ceratotropis V.subramaniana is more morphologically similar with V.radiata than V.mungo.2. Based on the high transferability and polymorphism of 57 adzuki bean SSR primers, the analysis of all species suggest that,⑴80% of adzuki bean SSR primers are able to be amplified in other sepcies which is also useful for evolution inference;⑵section Ceratotropis can be divided into two subgroups—V. radiata / V.subramaniana subgroup and V. mungo subgroup. The intra-specific diversity of V.radiata is highest while the inter-specific genetic relationships are rather close in section Angulares;⑶the relationship of morphological and molecular distance is significantly high(r=0.78**);⑷the weedy races of adzuki bean studied in this research should be escaped forms of the cultigens.3. Analysis of ITS sequences and RNA secondary structures of ITS2 spacer using MEGA4.0 and mfold 3.0 softwares reveals that,⑴since ITS2-RNA secondary structure of V.angularis is selected as the model structure (mean structural identity of 96.03% )of other species and the transferability of adzuki bean SSR markers is relatively high, it is inferred that the adzuki bean is most envolved among all species which is in agreement with prevoius observations;⑵based on the high bootstrap value of the topology of NJ trees and the high similarity of RNA secondary structures, V.hirtella and V.trinervia may be the diploid genome donors of V.reflexo-pilosa;⑶in section Angularis the Kimura-2 evolution distance is extremely small between species, moreover, V.minima,V. nakashimae, V.riukiuensis and V.umbellata are closely related, thus they may be evolved from the same wild ancestor;⑷frequent gene flow occurred between subspecies of V. radiata. Therefore, wild forms of V. radiata should be classfied into weedy and'real'wild forms combined with the morphological traits.4. Morphological traits, SSR motifs and ITS sequence data allow us to identify a distinctive species as a wild form of V. unguiculata although its germination habit is hypogeal. It is not closely related with subgenus Ceratotropis, however, the high transferability of adzuki bean SSR markers(82%) and comparative genomic study still show the breeding potential of this species.