Using population genetics and parentage analysis to detect intergenerational movement distances of flaxleaf fleabane (<i>Conyza bonariensis</i>)

Abstract The mobility of a weed species is a strong determinant of the optimal management strategy, including whether area-wide management will be beneficial. In this paper, we examine the mobility and dispersal distances of flaxleaf fleabane [ Conyza bonariensis (L.) Cronquist; syn.: Erigeron bonariensis L.], widely regarded as a highly mobile weed. We sampled individual weeds from two regions and sampled the same sites in the following season to conduct parentage analysis and assess intergenerational dispersal distances. We find high values of F IS across populations consistent with mostly self-fertilization, but also relatively high genotypic diversity, suggesting that outcrossing does occur at low rates. We find evidence for long-distance dispersal (more than 350 km) and detect dispersal distances of up to 71 km and 36 km within each of the two regions using parentage analysis. We also find high spatial genetic structure within the Riverina region, with sites in 2021 genetically very similar to sites in 2020, indicating that local dispersal may be a more important driver of population genetics than long-distance dispersal, perhaps due to the high rates of seed production and self-fertilization. Glyphosate resistance was not spatially structured in C. bonariensis in these regions, highlighting the role of movement, and significant proportions of susceptible plants were found in both regions. The high levels of mobility, including over potentially long distances, indicate that the value of control and preventing weed seed set is likely to extend beyond the farm and offer “area-wide” benefit.