Breakdown of the Self-Incompatibility Character, S Mutations and the Evolution of Self-Incompatible Systems

Abstract

One of the purposes of this chapter is to describe the different types of modifications which can lead — spontaneously or after manipulation, from either physiological or genetic changes — to a breakdown, mutation or transfer of the self-incompatibility (SI) character. The physiological changes are always temporary and cannot be transmitted from one generation to the next. However, their actions, when they contribute to the promotion of inbreeding or to variations in mating relationships, may have important implications for the genetic structure and fitness of the population in which they occur. Genetic changes, however, may or may not be permanent and lead to a variety of different effects, including:

• The breakdown of the incompatibility barrier through inactivation, silencing or deletions (partial or complete) of the S locus or the modification of other major genes, polygenes or ploidy levels.

• The increase in S-gene expression.

• The modification of S specificity or the substitution of autogamy by allogamy.