PLANTING DENSITY INFLUENCES THE EXPRESSION OF GENETIC VARIATION IN SEED MASS IN WILD RADISH (RAPHANUS SATIVUS L.: BRASSICACEAE)

To determine the effects of density, genotype, and their interaction on individual seed mass in Raphanus sativus L., we replicated maternal and paternal families of seed across two planting densities in an experimental garden. Seeds were produced by a nested breeding design performed in the greenhouse. Among garden-raised plants, density had a strong negative effect on the mass of seeds produced. At low density, the identity of the greenhouse-grown maternal plants had a strong effect on F₂ seed mass, while in high-density plots, there were no significant parental effects on mean seed mass. Significant parental genotype density interactions contributed to variation in F₂ seed mass. Norms of reaction for each of the 15 paternal sibships illustrate paternal family density interactions. Three sibships exhibited significant declines in mean seed mass with increasing density; 12 sibships showed no change. Maternal family density interaction effects on seed mass were also detected; among maternal sibships, mean seed mass at low density was negatively correlated with mean seed mass at high density. These results demonstrate: a) planting density has a strong effect on mean individual seed mass produced by adults; b) density influences the magnitude of maternal effects on progeny phenotype; and c) genotype density interactions influence seed mass, potentially contributing to the maintenance of maternal genetic variation in seed mass in natural populations of wild radish.