(self sterility) The failure of gametes from the same plant to form a viable embryo. In angiosperms this is usually due to complex interactions between the pollen and stigmatic tissues. Self incompatibility caused by the stigmatic tissues is described as sporophytic while that due to the pollen tube is termed gametaphytic. It may be achieved by the prevention of pollen germination, the retardation of growth or the disorientation of the pollen tube, or by failure of nuclear fusion. Although self incompatibility is known to be genetically controlled (see S alleles
) the exact method by which the genetic information manifests itself is not clearly understood. Enzymes either on the pollen or stigma, antibodies and antigens, growth substances, or variable cell morphology may account for differential treatment of pollen grains on the stigma. Incompatibility is rarely total and usually develops as the stigma matures. Artificial crosses of normally incompatible lines can therefore be made by in-bud pollination, chemical treatment, or by stigma excision.