Genetic diversity and structure of the noxious alien grass Praxelis clematidea in southern China

Praxelis clematidea (Asteraceae), a plant species native to South America, is a noxious weed in southern China. We examined the genetic variation and population structure of 12 populations (76 individuals) of P. clematidea from Fujian, Guangdong, and Hainan Provinces in China using inter-simple sequence repeat (ISSR) analysis. From an initial set of 69 ISSR primers, 10 were selected which yielded 80 reproducible bands. Polymorphic bands (P) were 100%, Shannon's information index (I) was 0.4226, and Nei's gene diversity (H) was 0.2791. We infer that the high levels of genetic diversity exhibited by P. clematidea may have contributed to its invasiveness. Gene flow among populations was 2.4930, which has led to homogenization. The coefficient of population differentiation (Gst=0.1671) indicated low levels of genetic variation among populations and high levels of genetic polymorphism within populations. There was a negative correlation between population elevation and genetic diversity, while there was a significant positive correlation between genetic distance and geographic distance based on a Mantel test (r=0.5820, P<0.01). Some populations from different provinces clustered together in principal coordinate and UPGMA analyses indicating that human-mediated events may have contributed to the dispersal of the species.