Effects of Style Age on the Performance of Self and Cross Pollen in Campanula rapunculoides

Abstract

Self-Incompatibility (S-I) involves a complex set of interactions between the microgametophyte and the pistil resulting in the recognition and inhibition of self pollen. Because S-I is regulated by the action of one or more S-genes, plant scientists have tended to think of self-incompatibility as a qualitative trait: i.e., a species is either self-compatible or it possesses an S-gene and is self-incompatible. In reality, however, S-I is often a quantitative trait. Moreover, the degree of S-I is known, at least in some species, to vary among specific S-alleles, with the composition of the pollen load (pure self-pollen vs. mixtures of self and cross pollen), with external environmental conditions such as temperature, and with internal stylar conditions such as the age of the flower (e.g. Jenkins, 1931; Ascher and Peloquin, 1966; Dane and Melton, 1973; Fearon et al., 1983; Bowman, 1987; and Knox et al., 1987).