Diallel crosses reveal patterns of variation in fruit-set, seed mass, and seed number in Asclepias incarnata.

Plants from each of two populations of Asclepias incarnata ssp. incarnata were hand-pollinated in diallel crosses and seed number per fruit, mean individual seed mass per fruit and fruit-set were determined for the parental plants. Two diallels were performed on the glasshouse-grown plants, one involving six plants from one population and the other involving five plants from the second population. The contributions to total phenotypic variation from joint, maternal, paternal, and two types of interaction sources of variation were then estimated. Variance attributable to maternal effects, reflecting differences between maternal plants resulting from environmental or genetic factors or both, comprised 31.3-68.4% of total variance in seed mass, 20.5-37.1% of variance in seed number, and 0.7-7.5% of variance in fruit-set. Interaction effects that depended on the direction of the cross accounted for 7.3-46.5% of variance in seed mass and 31.4-39.1% of variance in seed number. These interaction effects are consistent with the hypothesis that maternal plants provision resources differently to seeds depending on the specific genotypes of the embryos they contain. In the analysis of fruit-set, interaction effects independent of the direction of the cross (combined variance) explained 22.9-78.0% of phenotypic variance. These effects could have several causes, including inbreeding depression, shared incompatibility alleles, or 'control' of fruit-set by zygotes via hormonal signals or patterns of resource acquisition.