Successful pollen dispersal modulates with flowering phase in field-hybridizing grasses

Abstract

Gene-flow between intensively and extensively farmed grass populations is an ongoing feature of agroecological landscapes, especially in Atlantic northwestern Europe. Adjoining population boundaries and in-field admixture of grass types via winter forage dispersal facilitates both in-field hybridisation and recruitment of immigrant seedlings. Here we examine the paternal hybridisation of one grass species (Lolium multiflorum, pollen donor) into the population of a second, fully interfertile, grass species (L. perenne, pollen receptor) via pollen-mediated gene-flow in an experimental field plot. Using weekly counts of successful pollination in 470 individual receptor plants based on paternity analysis in 4281 germinated F1 seedlings, we determined the extent of evident hybridisation (hybrid progeny that show some paternal morphology) and silent hybridisation (hybrid progeny that show no paternal morphology) over the course of floral anthesis. Co-dominant morphological traits in F1 progeny underestimated microsatellite-validated genetic hybridisation by approximately 30%, while background pollen competition dampened the overall rate of successful pollen donor pollination. Overall pollination from the donor plot followed a composite decline model. However over the course of floral anthesis the successful pollination pattern was changeable, and showed varying levels of affinity to three tested decline distribution models.