Determination of incompatibility genotypes in almond using first and second intron consensus primers: detection of new S alleles and correction of reported S genotypes

The work aimed to develop a reliable and convenient PCR approach for determining incompatibility S genotypes in almond. Initially, genomic DNAs of 24 accessions of known S genotype were amplified with novel consensus primers flanking the first and second introns of the S-RNase gene. The PCR products separated on agarose showed length polymorphisms and correlated well with the reference alleles S1-S23 and Sf. In addition, to improve discrimination between alleles of similar sizes, the same sets of primers but fluorescently labelled were used, and the products sized on an automated sequencer. These fluorescent primers were particularly informative in the case of the first intron, variation in the length of which has not been used previously for S genotyping in almond. Some reference alleles showed the same patterns with first and second intron primers, and others showed a microsatellite-like trace. Subsequently, the S genotypes of 26 cultivars not genotyped previously and of four of uncertain genotype were determined. An allele described in Australian work as putative S10 was shown to be a ‘new’ allele and ascribed to S24 and evidence of five more ‘new’S alleles was found, for which the labels S25-S29 are proposed. This PCR approach should be useful for genotyping in other Prunus crops.