Assessment of gene flow in white clover (Trifolium repens L.) under field conditions in Australia using phenotypic and genetic markers

White clover is one of the most important pasture legumes in global temperate regions. It is an outcrossing, insect-pollinated species with gene flow occurring naturally between plants. A 2-year study was conducted to assess the relationship between gene flow and physical distance in white clover under field conditions in southern Australia. White clover plants exhibiting a red leaf mark phenotypic trait acted as pollen donors to recipient plants lacking leaf markings at distances up to 200m distant from the donor plants. Progeny were scored for the dominant red-leafed phenotype and gene flow was modelled. Paternity was confirmed using simple sequence repeat markers. A leptokurtic pattern of gene flow was observed under conditions designed to measure maximised gene flow with the majority of pollination occurring in the first 50m from the donor pollen source. The combined use of simple sequence repeat and visual markers confirmed that there was also a white clover pollen source in addition to the donor plants. This research confirms the difficulty in ensuring absolute containment of gene flow in an outcrossing species grown in an environment when endemic populations are known to exist.