The two types of genetic control of pollen self-incompatibility

Frequently, plants accept only pollen that does not correspond to their own type. Pollen rejection is controlled by genes at a self-incompatibility locus (S-locus). A) Gametophytic: the pollen type is controlled by the haploid genotype of the pollen grains themselves. A plant heterozygous for two alleles of the S-locus produces pollen of two incompatibility types (S1/S2). Only pollen of the incompatibility type S3 is accepted. Other pollen is rejected during transmission in the style. B) Sporophytic: the incompatibility type of the pollen is controlled by the diploid S-locus of the plant that produces it. Dominance is possible (i.e. S2 dominant) and a plant produces pollen of only one pollen type. Such pollen cannot fertilize a plant with an S2 allele. Pollen is rejected on the stigma surface.

1 - Self-incompatibility (after Silvertown and Charlesworth 2001)