Patterns of Diversity of the S and M Loci in Tunisian Apricots (Prunus armeniaca L.): Identification of Pollen-Part Mutations Conferring Self-Compatibility

Self-(in)compatibility (SI) is a genetic barrier developed by flowering plants to prevent self-pollination and promote outcrossing. SI is one of the most important traits in stone fruit breeding and particularly in apricot. Indeed, researchers focused their interests on identifying and selecting self-(in)compatible apricot parents for breeding programs and cultivars for the installation of new plantations. In this context, SI was studied in a set of 65 Tunisian apricot accessions focusing on both S and M loci targeting the genes, S-RNase, SFB, and ParMDO, with different primer combinations. The amplification of the first and the second intron of the S-RNase gene allowed the identification of nine different S alleles. The S₇ allele which is reported to be present only in Southern Europe and North Africa regions was the most frequent occurring in 24 genotypes. Moreover, self-pollination tests and amplification of the SFB and ParMDO gene insertions (S_C and m haplotypes) producing pollen-part mutations (PPMs) that confer self-compatibility (SC) allowed us to correlate the presence of these two independent PPMs with SC for the first time within Tunisian apricot germplasm. Overall, nine accessions were found to be self-compatible carrying at least one self-compatible haplotype. The distribution of S alleles in the analyzed accessions supported the introduction of apricot to North Africa from the Irano-Caucasian region. Moreover, the detection of the self-compatible ParMDO m haplotype in Kairouan accessions similar to Spanish cultivars confirmed gene flow between Western European and North African apricots. All these results may provide relevant information for apricot breeding and production.