Sexual selection has been shown to be a powerful evolutionary force in animals, however in plants it has been more controversial. Research with the weedy annual Raphanus sativus has demonstrated that nonrandom mating can occur in greenhouse plants. We asked whether this nonrandom mating can occur under a wide range of conditions, including conditions that might occur in the field. To answer this question we constructed a continuum of treatments including variation in both maternal condition and pollen load size. Maternal condition was varied by altering the watering regime. Pollen load size was varied from 30 to 400 pollen grains per stigma. Seed siring success was influenced by the pollen donor and the maternal family. Additionally, maternal condition and pollen load size had an effect on seed siring success. The results suggest that there is a threshold below which nonrandom mating does not occur.

Key words: nonrandom mating, pollen load size, Raphanus sativus