Genetic characterization of pear germplasm of Lazio, Italy

Pear cultivation has a long tradition in Italy, the EU's largest pear producer. Among the Italian regions, Lazio is particularly rich in pear local varieties of great agronomic interest. This germplasm represents a priceless source of genetic diversity and, thus, an excellent tool to possibly cope with the consequences of the climatic change. In this study, we attempted to genetically characterize a collection of 93 pear accessions, collected throughout the five provinces of the Lazio region. The analysis has been conducted by using a highly polymorphic set of 9 SSR markers selected from the literature. The data collected were used to estimate the genetic diversity, to identify the genetic structure and relationship among the accession, and to detect possible cases of synonymy. The microsatellites showed a high polymorphism information content (PIC), on average equal to 0.74. Furthermore, SSR markers were able to detect the occurrence of triallelic loci. In concordance with previous studies where the triploidy on pear was confirmed, we hypothesized the presence of 32 putative triploid genotypes out of 93. The Bayesian model-based Structure analysis firstly categorized the accessions into two main distinct clusters (K=2) and a second subdivision resulting in 3 clusters (K=3) was found, supporting as many ancestral groups. In any case, the population structure analysis did not cluster samples based on ploidy levels: this would suggest that the polyploidization events are quite recent. Those samples showing admixed patterns were instead hypothesized to be a consequence of hybridization events that took place in Europe throughout the centuries. The SSR analysis also revealed 8 cases of synonymy. In half of cases, it was somehow expected since the accessions that proved 100% of genetic similarity also shared the same nomenclature. On the contrary, in four occasions, synonymy cases were observed (i.e. accessions with different names but identical molecular profiles). By taking advantage of molecular markers, we were able to partially decipher the genetic complexity characterizing the Pyrus accessions of the Lazio germplasm.