The Expression of Self-compatibility in Almond May Not Only Be Due to the Presence of the Sf Allele

ADDITIONAL INDEX WORDS. Prunus amygdalus, PCR analysis, sequencing, pollination ABSTRACT. The pistil (S-RNase) and the pollen (S-haplotype-specific F-box protein (SFB)) components of the Sf allele, presumably conferring self-compatibility in almond {Prunus amygdalus Batsch (syn. P. dulcis (Mill.) D.A. Webb)}, were identified and sequenced in 'Ponc x', a local Spanish almond cultivar, confirming their identity with the published sequences of these components. Despite the presence of the Sf allele, the 'Ponc x' phenotype was self-incompatible as confirmed by different pollination tests, including self pollen tube growth, fruit set after self-pollination, and fruit set in bagged branches. However, the pistil and the pollen of 'Ponc x' were fully viable when pollinated by a cross- compatible pollen or used on a cross-compatible pistil. The fact that 'Ponc x' presents two different S-proteins with RNase activity may indicate an active function of its Sf-RNase, whereas in the self-compatible almond cultivars thus far studied, the Sf-RNase has been inactive. This activation indicates that the presence of the Sf allele may not be the exclusive source of self-compatibility in almond, and other factors may also be involved in the expression of almond self-compatibility.