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

Abstract

The pistil ( S -RNase) and the pollen [ S -haplotype-specific F-box protein (SFB)] components of the S f allele, presumably conferring self-compatibility in almond { Prunus amygdalus Batsch [syn. P. dulcis (Mill.) D.A. Webb]}, were identified and sequenced in ‘Ponç’, a local Spanish almond cultivar, confirming their identity with the published sequences of these components. Despite the presence of the S f allele, the ‘Ponç’ 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 ‘Ponç’ were fully viable when pollinated by a cross-compatible pollen or used on a cross-compatible pistil. The fact that ‘Ponç’ presents two different S -proteins with RNase activity may indicate an active function of its S f -RNase, whereas in the self-compatible almond cultivars thus far studied, the S f -RNase has been inactive. This activation indicates that the presence of the S f 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.