Almond Self-Incompatibility Genetics: Recent Progress and Future Prospects

Self-incompatibility in almond is of the gametophytic type and controlled by a multigene complex named the S locus, expressed in the pistil (S-RNase) and in the pollen (SFB protein). Despite of being described as a self-incompatible species, self-compatible almond accessions have been identified. As a result of the intensive research carried out in the last years on self-incompatibility (SI) genetics of this and other Prunus species, efficient PCR primers were designed. These primers allowed the molecular identification and characterization of several S-haplotypes in almond. This information resulted very useful to update the table of cross-incompatibility groups and also for phylogenetic studies in Prunus. Moreover, these molecular tools are routinely applied in some almond breeding programmes for the early selection of self-compatible individuals. Since the identification of self-compatible almonds, several studies have tried to explain this failure in the functioning of the SI system. Recent studies have pointed out that unknown components other than S-RNase and SFB proteins should be involved in the SI system. Nowadays the efforts are focused on the identification of these other genes/proteins and their possible interactions by carrying out genome studies and comparative proteomic assays.