Genetic diversity and relationships within and among Onobrychis species using molecular markers

Little is known about the taxonomic relationships of the genus Onobrychis (Fabaceae). To study inter- and intraspecific variations and the relationships among the species, 102 accessions (33 species) of the genus Onobrychis were evaluated using 22 inter-simple sequence repeat (ISSR) markers. Almost all the species belonging to the section Onobrychis clustered together. A similar pattern was found with the species belonging to the section Hymenobrychis, while those of the section Lophobrychis did not cluster together. The results indicate that the section Lophobrychis has a comparatively derived organization that can be attributed to the differences in their taxonomic delimitation. Geographical pattern was found to be associated with the genetic diversity within the species. Principal coordinates analysis (PCoA) indicated a high association among the sections Lophobrychis, Heliobrychis, and Hymenobrychis. Thus, the present subgeneric classification of Onobrychis (Onobrychis and Sisyrosema) was not supported. The results based on Nei's similarity suggest that some species in the genus Onobrychis (especially O. Altissima) might have been outcrossing with reproductive ability with O. Viciifolia. Our results suggest that species with x = 7 chromosome are closer to O. Viciifolia than to those with x = 8. Therefore, a base number n = 8 can be assumed for this genus (within Onobrychis genus basal), changing to 7 through aneuploid loss.