XVI International Botanical Congess

Genetic systems of homomorphic self-incompatibility prevent self-fertilization through recognition and rejection of pollen that express specificities held in common with the seed parent. Surveys of natural populations have revealed diverse patterns in the level of variation and genealogical relationships among genetic variants segregating at S-loci, which regulate self-incompatibility. Among the most important determinants of these aspects is the rate at which distinct mating specificities appear and become incorporated into natural populations. Aspects that influence the rate of diversification of S-specificities include the effects of enforced heterozygosity at the S-locus on other genomic regions, particularly those held in close physical linkage with the S-locus, and coevolution between the pollen and stylar components of the recognition and rejection reactions. The nature of interactions among evolving S-haplotypes and their implications for the evolution of mating systems will be addressed.