Genetic diversity and genetic differentiation of invasive weed Xanthium italicum in China.

Xanthium italicum is an aggressive weed found worldwide. Despite several ecological, morphological, and physiological research on its invasion mechanism, the mechanism of its successful invasion has not been revealed from the viewpoint of population genetics. Thus, we aimed to evaluate the genetic variation within and among populations of the alien invasive weed X. italicum in China, and to provide a theoretical basis for its invasion mechanism. For that, we employed inter-simple sequence repeat (ISSR) markers to explore the genetic diversity and genetic differentiation of 185 individuals sampled from 10 populations. Eight selected primers yielded a total of 76 bright and discernible bands. X. italicum showed an intermediate genetic diversity at the population level (percentage of polymorphic loci (PPL) = 60.26%, Nei's genetic diversity (H) = 0.2098, Shannon's information index (I) = 0.3129). However, the genetic diversity at the species level was significantly high (PPL = 100%; H = 0.3673; I = 0.5425). The coefficient of gene differentiation (GST, 41.4%) and analysis of molecular variance showed that genetic differentiation mainly occurred within populations. The estimated gene flow (Nm, 0.7085) and Mantel test indicated that genetic differentiation in the populations may primarily come from genetic drift and anthropogenic activities. Our results revealed the high genetic diversity of X. italicum, which may help explain its invasion success in China. This knowledge may contribute to the efforts for decreasing and eventually stopping X. italicum invasion in China.