Genetic diversity and clonal vs. sexual reproduction in Fallopia spp. (Polygonaceae)

Although fundamental to the study of invasion mechanisms, the relationship between mode of reproduction and plant invasion is not well understood. Fallopia japonica (Japanese knotweed), a highly aggressive invasive plant in both Europe and North America, serves as a model species for examining this relationship. In Britain, F. japonica var. japonica is a single female clone reproducing solely through vegetative growth or obligate hybridization with other Fallopia spp. In the U.S., however, there is more evidence for sexual reproduction. Here, simple sequence repeat (SSR) markers were developed, and three Massachusetts populations were sampled at regular intervals. The amount of sexual and clonal reproduction in each population was determined based on within-population genetic diversity. Clonal growth was apparent, but the populations together contained 26 genotypes and had evidence of sexual reproduction. One genotype that was present in all populations matched the single aggressive British clone of F. japonica var. japonica. Also, a potentially diagnostic marker for the F. sachalinensis genome provided evidence of inter- and intraspecific sexual reproduction and introgression. These differences observed in U.S. populations compared to European populations have significant implications for management of Fallopia spp. in the U.S. and underscore the importance of regional studies of invasive species.