CROP-WEED HYBRIDIZATION IN RADISH (RAPHANUS SATIVUS) - EFFECTS OF DISTANCE AND POPULATION-SIZE

Crop-weed hybridization rates between an agricultural plot of cultivated radish and surrounding stands of wild radish (both Raphanus sativus L.) were measured. The crop and weed were fixed for alternate isozyme alleles to allow for identification of hybrids through progeny testing. Weed populations were planted in three sizes (one, two, and nine plants) and at three distances (1, 200, and 400 m) from the crop. Hybridization rates declined with increasing linear distance between crop and weeds. When observed rates of hybridization were corrected for frequency of recipient weeds, the potential level of hybridization actually increased with distance. The effect of population size on rate of hybridization was significant; the direction of the effect was dependent on crop-weed distance. The observed relationship between population size and hybridization rates was not predictable according to current pollination ecology theory.