Self-(in)compatibility in ‘AS-1’, a Local Spanish Almond Cultivar

The finding of new self-compatible cultivars in local population is a breeder’s objective in order to increase the sources of self-compatibility for the almond (Prunus amygdalus Batsch) breeding programmes. ‘AS-1’, a local Spanish selection, was considered to be self-compatible according to its self pollen tube growth and was incorporated in the almond breeding programme of Zaragoza as a source for this trait. However, both pollen tube growth and fruit set after self-pollination have shown that this selection is self-incompatible. The PCR analysis using specific and consensus primers revealed that its genotype is S8S12, where both alleles control selfincompatibility and do not confer self-compatibility in almond. The field crosses of ‘AS-1’ and ‘Marcona Flota’, of the same S genotype, were incompatible, confirming the S genotype of ‘AS-1’ determined by PCR analysis. The sequencing of the SFB S haplotype showed that 'AS-1' presents SFB and SFB. Moreover, the absence of any notable deletion or insertion upstream from the HVa and HVb regions in the sequence of the SFB and SFB S-haplotypes confirm their identity. All these results, including pollination tests, PCR analysis and cloning and sequencing of the S alleles of ‘AS-1’, indicate that this local selection is self-incompatible. INTRODUCTION The limited number of sources for self-compatibility utilised in almond breeding programmes (Socias i Company, 2002) recommended the search for new self-compatible forms among the different almond populations, mainly in local forms, such it happened with the local cultivars of the Puglia region in Italy (Grasselly and Olivier, 1976). As a result of an initial search, ‘AS-1’ was noticed in Tamarite de la Litera, Huesca province, Spain, as a single late-blooming tree, isolated from other simultaneously blooming almond trees and setting fruit every year, thus presumably self-compatible. Herrero and Felipe (1975) conducted controlled field pollinations and pollen tube growth observations in several cultivars and reported that ‘AS-1’ was self-compatible. ‘AS-1’ was included in the Zaragoza breeding programme and Socias i Company and Felipe (1988) reported a 3:1 (SC:SI) distribution in the progeny of the cross ‘Tuono’ × ‘AS1’, as expected in a cross involving two different heterozygous self-compatible cultivars. When ‘AS-1’ was open-pollinated, these authors found four self-compatible seedlings in a progeny of 15, thus presumably showing a self-compatible behaviour both in expression and transmission.