S-genotype identification, genetic diversity and structure analysis of Italian sweet cherry germplasm

In this study, 186 local sweet cherry accessions from 12 Italian regions, plus eight reference accessions, were analysed for the first time, using 13 microsatellite markers. Moreover, their S-incompatibility genotypes were identified with consensus primers for the S-RNase and SFB genes. A total of 161 unique genotypes were found; 18 groups of synonyms, along with the discovery of cases of misidentification. The average number of alleles per locus was 9.7, the mean expected heterozygosity (He) was 0.63, the mean observed heterozygosity (Ho) was 0.65 and the mean polymorphic information content (PIC) was 0.58. The structure analysis revealed the presence of six populations, which reflected in some cases geographical areas, the exchange of material among regions and introduction of material from abroad. A total of 17 different S-alleles were found, combined in 24 incompatibility groups of the 47 reported so far. Furthermore, 10 new incompatibility groups, from XLVII to LVI, were identified. Seven genotypes with unique S-allele combinations were included in the pollen donor group 0. The mutant allele of the pollen SFB5′ was found in early ripening genotypes from Sicily and Sardinia. The variability of SSRs present in both introns of the allele S13 was also explored; new combinations of variants were found and some accessions presented SSR variants typical of wild cherry. It is evident that the Italian sweet cherry germplasm collection represents a relevant source of genetic diversity that needs to be preserved for future breeding programmes.