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 w ere hand-pollinated in diallel crosses and seed number per fruit, mean indi vidual seed mass per fruit and fruit-set were determined for the parental p lants. Two diallels were performed on the glasshouse-grown plants, one invo lving six plants from one population and the other involving five plants fr om the second population. The contributions to total phenotypic variation f rom joint, maternal, paternal, and two types of interaction sources of vari ation were then estimated. Variance attributable to maternal effects, refle cting differences between maternal plants resulting from environmental or g enetic 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 accoun ted for 7.3-46.5% of variance in seed mass and 31.4-39.1% of variance in se ed number. These interaction effects are consistent with the hypothesis tha t maternal plants provision resources differently to seeds depending on the specific genotypes of the embryos they contain. In the analysis of fruit-s et, 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 incompatibili ty alleles, or 'control' of fruit-set by zygotes via hormonal signals or pa tterns of resource acquisition.