Identification of Self-Incompatibility Genotypes in Iranian Almond Cultivars

Almond is an economically important fruit tree species in which the commercial part is the seed, making fertilization essential for production. Due to its general self-incompatibility (a genetic barrier that avoids self-fertilization), two or more cross-compatible cultivars must be grown in the same orchard. Thus, determination of the self-incompatibility genotype is a very useful tool for orchard design and for parental choice in breeding programs. The S-RNase alleles of 62 almond cultivars grown in Iran were identified by PCR, using combinations of the consensus primers PaConsI-F, EM-PC1consRD, EM-PC2consFD, EM-PC3consRD, and EM-PC5consRD. Sixteen cultivars of European, American, and Asian origin were also included in the analysis as references for the 30 S-RNase alleles already characterized in almond. Initially, PCR products obtained with the primer set EM-PC2consFD +EM-PC3consRD were run on agarose gels alongside the reference cultivars. When inconsistencies such as amplification of only one band or unclear band size correspondence were found, PCR using the primer sets PaConsI-F +EM-PC1consRD or PaConsI-F + EM-PC5consRD was performed. In most cases, the results showed two bands that matched the size of known S-RNase alleles. However, in 13 cultivars eight bands differing in size from those of the reference cultivars were identified. These bands were considered to correspond to new S-RNases. The S genotype of most cultivars differed from those of the established cross-incompatibility groups and, although the vast majority could be classified in the universal group O, some showed an identical genotype, so that nine new groups could be proposed.