Identification of self-incompatibility alleles in almond and related Prunus species using PCR

Self-incompatibility in almond is of the gametophytic type and acts to prevent self-fertilization. This trait is controlled by a single locus with multiple codominant alleles and is expressed within the styles as S-RNases. These glycoproteins are responsible for the inactivation of self-pollen tube growth. Self-incompatibility alleles (S-alleles) can be identified through controlled crosses with a series of known S-genotypes. Molecular methods have recently been developed allowing both stylar S-RNases electrophoresis and S-allele specific amplification using PCR. In this study, the identification of S-genotypes of almond cultivars and related Prunus species was achieved using the specific PCR primers AS1II and AmyC5R. Plant material analyzed included 18 almond cultivars from different geographical origins and 12 Prunus species. Results identify 8 unique S-alleles in almond and 6 in related Prunus species. Findings also clarify the genetic relationships among almond and related Prunus species. The nucleotide sequences of these primers appear to be highly conserved in almond and its close relatives. The applications of these PCR markers in the UC-Davis almond-breeding program are discussed.