Heritability of stigma position and the effect of stigma‐anther separation on outcrossing in a predominantly self‐fertilizing weed, Datura stramonium (Solanaceae)

A polymorphism for anthocyanin production was used as a genetic marker to document the relationship between anther–stigma separation and outcrossing rate in the predominantly self‐fertilizing weed Datura stramonium. White‐flowered plants that differed in anther–stigma separation were placed into populations consisting exclusively of purple‐flowered plants. Self vs. outcross origin of progeny was evident in the hypocotyl color of the seedlings. Outcrossing rates measured for single flowers were significantly positively correlated with anther–stigma separation, albeit with some scatter around the regression line, especially for flowers with exserted stigmas. We also performed an 8 × 8 diallel cross to determine whether anther–stigma separation is genetically determined. Heritability in two field plots was ∼0.3 and in the greenhouse was ∼0.2. Maternal effects, epistasis, and dominance appeared to be relatively unimportant. Genotypes performed consistently across the three environments, although total plant size varied more than fivefold. It appears that the mixed‐mating system of D. stramonium has a heritable basis and would be capable of responding to selection.