Inter specific Incompatibility
This type of incompatibility is characterized by the prevention of fusion of gametes between members of different species. The incompatibility factors also operate after fertilization and cause eventual breakdown and failure of embryo development. The factors that prevent seed set following inter specific crosses have not been worked out. It is however apparent that rejection reaction may operate at any level. In Petunia the morphological abnormalities of the pollen tube are similar in both self and inter-generic incompatibility.
The inhibition may result from unilateral incompatibility, or incongruity or a passive rejection may operate. Inter specific incompatibility involves non-proteinaceous substances besides the stigma surface proteins. Phenolics and carbohydrates also seem to play an important role. It is believed that more than one gene at different loci controls the inter specific incompatibility. In crosses between incompatible species either fertilisation does not occur or the hybrid embryo aborts due to either inadequate development of endosperm or lack of support from endosperm.