Constancy of population parameters for life history and floral traits in Raphanus sativus L. I. Norms of reaction and the nature of genotype by environment interactions

We observed norms of reaction for life history and floral traits in Raphanus sativus L. (wild radish: Brassicaceae) among genotypes raised in three planting densities. In the greenhouse, we used a nested breeding design to produce F1 seed representing 60 maternal plants and 15 pollen donors grown from field-collected seed. Eighteen hundred-seeds were grown in three planting densities in an experimental garden. For each individual, we recorded survivorship, germination date, flowering date, petal area, ovule number, pollen production, and the mode of individual pollen grain volume/flower. Planting density had a strong effect on survivorship, but differential mortality among genotypes was not density-specific. Two-way ANOVAS (block and density as class variables) were conducted on each paternal sibship to detect significant differences among densities with respect to mean phenotype. Among the 15 paternal genotypes, 12 exhibited significantly faster germination in the high-density plots. Three paternal families exhibited significantly delayed flowering at high-density. Two paternal families exhibited significant effects of density on petal area, but in opposite directions. Two paternal families had significantly lower ovule production at high-density. No paternal families exhibited significant effects of density on pollen production or pollen-grain volume. Strong differences among genotypes with respect to the effects of density on phenotype indicate genetic variation in the plastic response to density for these traits. Three-way ANOVAS of each density treatment measured the effects of block, paternal family and maternal family on phenotype; significant paternal effects indicated the presence of significant additive genetic variance (VA) in the measured trait. The ability to detect VA and maternal effects nested within paternal genotypes in most of these traits was density-specific.