Sporophytic and Gametophytic Self-Incompatibility
Besides the categories based on morphology, self incompatibility can be further classified into sporophytic or gametophytic types depending on the origin of factors that determine the mating types on the pollen side.
i) Gametophytic self-incompatibility (GSI) is governed by the genotype of pollen (male gametophyte) itself, e.g., Poaceae, Liliaceae, Solanaceae, Fabaceae, and Commelinaceae.
ii) Sporophytic self-incompatibility (SSI) the genotype of the sporophytic tissue which donates the pollen controls the incompatibility process, e.g., Asteraceae, Brassicaceae and Convolvulaceae.
Other characteristics of GSI and SSI systems are described in Table. A correlation has been established between the type of self-incompatibility, pollen cytology, and the site of inhibition. Generally, species that shed pollen at the 2 - celled stage are credited with gametophytic incompatibility (inhibition occurring in style) while those shedding 3-celled pollen show sporophytic incompatibility (zone of inhibition on stigma). Additionally, taxa having dry type of stigma are associated with sporophytic incompatibility whereas those with wet stigma show gametophytic incompatibility. There are a few exceptions to these correlations.