Genetic diversity of Caragana species of the Ordos Plateau in China

摘要

Plants of the genus Caragana (Fabaceae) are dominant shrub species of high ecological and economic importance on the Ordos Plateau in China. Due to natural environmental variability and anthropogenic impacts, Caragana pastures have experienced severe degradation, which has decreased their carrying capacity. In this study, we investigated the genetic diversity of eight Caragana species (C. purdomii, C. opulens, C. stenophylla, C. intermedia, C. korshinskii, C. roborovskyi, C. tibetica and C. brachypoda) on the Ordos Plateau by using ISSR markers. The results reveal high genetic diversity of all the species, with the percentage of polymorphic bands (PPB) reaching 100%. However, interspecific differences in genetic diversity within the genus were significant, as indicated by higher levels of genetic diversity of C. stenophylla, C. tibetica, C. intermedia, C. korshinskii and C. roborovskyi (PPB > 86%) when compared to the C. brachypoda with the lowest genetic diversity (PPB = 42.86%). Caragana brachypoda showed the lowest genetic similarity with and largest genetic distance from other taxa of the genus. Caragana tibetica had higher genetic diversity than C. roborovskyi. A large genetic distance was found between C. roborovskyi and C. tibetica, although the two species belong to Ser. Tragacanthoides and grow in a semidesert area. Such differences in genetic structure may be the reason for large areas occupied by C. tibetica, whereas C. roborovsky has rather limited distribution in the semidesert area. Caragana intermedia had high genetic diversity and a large genetic differentiation between intraspecific populations implying strong adaptability of the species to environmental fluctuations and selection capabilities. There was an obvious gene flow between C. intermedia and C. korshinskii, suggesting possible hybridization between these species is consistent with ecological variability, which may be important characteristics of Caragana plants in terms of molecular variation in the ecotone of Ordos plateau. Our results provide a molecular basis for sustainable management, utilization and conservation of Caragana plants on the Ordos plateau.