Self-Incompatibility of Almond Species

Commercial almond cultivars (Prunus dulcis) are self-sterile, expressing gametophytic self-incompatibility and requiring insect pollinators for cross-pollinations. Self-fruitfulness is a major objective of almond breeding programs, and sources have been identified. Two are peach, including cultivated peach, Prunus persica, and the wild Prunus mira. A third source for self-compatibility is the wild almond species Prunus webbii. Historical and molecular evidence indicates that self-compatible heirloom cultivars have arisen as landraces from natural introgression between cultivated almonds and wild plantings of Prunus webbii. Self-incompatibility/compatibility is regulated by a single gene (S-locus) with multiple alleles. This gene consists of at least two factors (alleles) controlling pollen and pistil self-recognition. To identify different S-alleles in cultivated almonds and related species, researchers have used both chemical and molecular methods, including degenerate primers, general primers, allele-specific primers, and multiplex primers.