Homomorphic Types - Intra specific Incompatibility
It is characterized by morphologically indistinguishable mating types within a species. A proper breeding is required for their recognition. This kind of incompatibility operates in more than 250 genera belonging to 71 families of angiosperms. It operates through multiple alleles (as many as 45 alleles are already reported from 500 plants) of S-gene. Pollen grains with one S-allele common with one or both S-allele/s of pistil is incompatible, it is therefore conceivable that on pollen side the haploid gametophyte controls incompatibility. The S-allele my express a relationship of dominance or independence in pollen and/or pistil.