The field of self-incompatibility research is at present highly dynamic, and an understanding of the mechanisms of operation of the two most widespread systems is almost within our grasp. This review brings together information on the main types of self-incompatibility systems, outlines the potential benefits of the ability to manipulate self-incompatibility systems to agriculture, and explains how recent breakthroughs made in this field may allow the plant breeders to have this capability within the foreseeable future.
Self-incompatibility (SI) is a genetic system possessed by many flowering plants. Indeed, SI has been reported in 66 plant families, representing every major phylogenetic line of the angiosperms (Brewbaker 1957), and it can be defined as “the inability of a fertile hermaphrodite seed plant to produce zygotes after self-pollination” (Lundqvist 1964, p. 222). The significance of SI in the evolutionary context cannot be overstated, for its possession leads to obligate outbreeding and the maintenance of heterozygosity within a species (Stebbins 1950).
Among crop and ornamental plants, most of the perennial grasses (Gramineae), forage legumes (Fabaceae), and members of the Brassicaceae (cabbage, kale, and so forth), Asteraceae (sunflowers, cosmos), Rosaceae (apples, cherries, pears, and so forth) and Solanaceae (petunia, potato, tobacco, and tomato relatives) have SI mechanisms of varying kinds and degrees of effectiveness.
SI presents contrasting prospects to plant breeders. On one hand it will frustrate efforts to produce homozygous lines, but on the other it provides a way to hybridize two lines without emasculation, nuclear or cytoplasmic sterility, or resorting to gametocides.