Characterisation of microsatellite loci in Sardinian pears (Pyrus communis L. and P. spinosa Forssk.)

The Sardinian pear germplasm is an important resource of genetic diversity that can be used for increasing data on European pear germplasm, to optimise the efficiency of the association studies within the genome and to identify genomic regions that control the main horticultural traits. A set of 108 Sardinian pear genotypes, composed of 81 Pyrus communis cultivars, 24 wild populations of P. spinosa and three international reference cultivars, was analysed using nine SSR markers to assess the genetic diversity of Sardinian pears, determine their genetic structure and study the cases of synonymies and homonymies. The comparison of SSR profiles indicated four groups of diploid accessions with the same SSR profile. The alignment with the Sardinian dataset, pointed out a clear genotype distinctiveness. For all studied SSR loci, 15 specific rare alleles were identified, with a minimum of two alleles found in the database of analysed accessions for the SSRs EMPc11 and EMPc117. The overall allelic diversity revealed a high polymorphism in the analysed Sardinian germplasm. The structure analysis allowed us to identify four gene pool groups (Sardinian cultivars, Japanese cultivars, late-ripening cultivars and, the most famous, standard cultivars). These results were confirmed by Evanno's △k statistical analysis which has shown unequivocally that k = 4 (△k = 150) is the most likely stratification level of the cluster. The Q values of P. communis and P. spinosa accessions have confirmed an allelic interchange between wild and cultivated genotypes.