Late-acting self-incompatibility in Ipomopsis tenuifolia (Gray) V.!Grant (Polemoniaceae)

Several different self-incompatibility ( SI) syndromes have been previously reported from Polemoniaceae, including differences in genetic control, timing of the response, and the location of pollen tube inhibition. In order to examine the evolutionary linkage between genetic control and site of pollen tube inhibition, crossing experiments and microscopic analyses were performed on an additional species of Polemoniaceae, Ipomopsis tenuifolia. Thirteen individuals from a natural population were used for the parental crosses; three F-1 full-sibling arrays were grown to maturity. Strong self-incompatibility was found in the parental population on the basis of significant differences in the percentages of seed set in self-versus outcross matings. In the F1 arrays, none of the outcrosses or backcrosses was completely incompatible, leading to a large number of mating types. On the basis of the number of mating types in the F1 arrays, self-recognition in this species must be based on full allelic matching of at least three loci. Pollen tubes were observed inside the ovary after both cross- and self-pollination using SEM and fluorescent microscopy, suggesting that self-pollination recognition takes place in the ovule, representing a late-acting SI system. The large number of different SI mechanisms reported in the Polemoniaceae suggest that this family may be particularly labile in its breeding system.