IDENTIFYING POLLEN INCOMPATIBILITY GROUPS IN CALIFORNIA ALMOND CULTIVARS

Six cross-incompatibility groups, which contain most of commercially important California almond cultivars [Prunus dulcis (Mill.) D.A. Webb, syn. Prunus amygdalus Batch], and their self-incompatibility (S) allele genotypes are identified. Incompatibility groups include 'Mission' (S(a)S(b)), 'Nonpareil' (S(c)S(d)), and the four groups resulting from the 'Mission' X 'Nonpareil' cross: (S(a)S(c)), (S(a)S(d)), (S(b)S(c)), and (S(b)S(d)), as represented by 'Thompson', 'Carmel', 'Merced' and 'Monterey', respectively. All seedlings from the 'Mission' X 'Nonpareil' cross were compatible with both parents, a result indicating that these two cultivars have no alleles in common. Crossing studies support a full-sib relationship for these progeny groups and the origin of both parents from common germplasm. Cultivars in these six groups account for almost-equal-to 93% of present California production, a result demonstrating a limited genetic base for this vegetatively propagated tree crop.