Stylar ribonucleases in almond: correlation with and prediction of incompatibility genotypes

To clarify incompatibility relationships among almond cultivars, 35 were analysed for stylar ribonucleases, which have previously been shown to correlate with incompatibility S alleles. Stylar proteins were extracted and separated electrophoretically and the zymograms compared with ladders of ribonucleases corresponding to the 12 S alleles previously reported. Sixteen cultivars showed a band corresponding to two of the known ribonucleases, 17 showed one known ribonuclease and one 'new' band, and two showed two new bands. Twelve new ribonucleases were detected; 11 were attributed to new S alleles (S (13) to S (23) ) and a mutant form of S (7) was attributed to S (7A) . Genotypes were proposed for nine cultivars of five incompatibility groups that had not been genotyped previously, VII, X, XI, XII and XIII. Twenty-four cultivars of unknown incompatibility relationships were provisionally genotyped: six of these could be assigned to existing groups and two new groups were established, XIV and XV, along with group O of cultivars with unique genotypes. Test crosses confirmed that eight pairs of cultivars showing similar zymograms were indeed cross-incompatible, including the two representatives of each of the two new groups. Virtually all self-incompatible cultivars of known genotype are listed in a table. The data should be useful for planning cultivar combinations for orchards and for designing crosses for breeding programmes.