Self-incompatibility (SI) is the failure of a fertile plant to set seeds when fertilized with its own pollen. It is a physiological mechanism, with a genetic basis, which promotes allogamy and has drawn geneticists and plant breeders’ attention. Nowadays, the research has put emphasis on the identification and understanding of the molecular and cellular processes leading to the recognition and rejection of the self-incompatible pollen, including the identification, localization and sequencing of proteins, enzymes and genes involved. There are two types of SI, gametophytic (GSI) in which the pollen specificity is determined by the S allele of the pollen grain (gametophyte) haploid genome, and sporophytic (SIS), where the pollen specificity is determined by the diploid genotype of the adult plant (sporophyte) that generated the pollen grain. SIS may be homomorphic, when there are no floral modifications related to the SI process, or heteromorphic, when floral modifications occur together with the SI process. The SI reaction may occurr from pollen germination impairing up to pollen tube breakdown. The existence of SI in economically important plants may be very important, being very positive in some cases or a burden in others, depending on the plant part harvested (vegetative or reproductive) and its mode of reproduction, sexual or asexual. SI has been employed in plant breeding for many years, but there is a gap between theoretical knowledge, such as genetic and molecular basis, and utilization in plant breeding programs.
self-incompatibility; plant breeding