What is Self-incompatibility – Definition?

Self-incompatibility is a general name for all those genetic mechanisms in flowering plants / angiosperms, which prevent selfing. It is phenomenon with which a plant with functional pollen fails to set seed when self pollinated. It is incompatibility between the pollen and the stigmas of the same plant.

General features of Self-incompatibility

  • Prevents selfing and promotes outbreeding so increases the probability of new gene combinations
  • Causes may be morphological, physiological, genetical or biochemical
  • Normal seed set on cross pollination
  • May operate at any stage between pollination and fertilization
  • Reduces homozygosity
  • In plants, self-incompatibility is often inherited by a single gene (S) with different alleles (e.g. S1, S2, S3 etc.) in the species population

Classification of Self-incompatibility

Self-incompatibility is classified on the basis of various criteria listed as follows

Criteria Types
Flower morphology Heteromorphic self incompatibility Distyly
Homomorphic self incompatibility Sporophytic self ncompatibility
Gametophytic self incompatibility
Genes involved (number) Monoallelic (governed by single gene)
Diallelic (governed by two genes)
Polyallelic (governed by many genes)
Cytology of pollen Binucleate (pollens with two nuclei)
Trinucleate (pollens with three nuclei)
Expression site Ovarian (expression site is ovary)
Stylar (expression site is style)
Stigmatic (expression site is stigma)