Genetic and ploidy diversity of pear (Pyrus spp.) germplasm of Friuli Venezia Giulia, Italy

Abstract

Ancient germplasm represents a reservoir of traits and genes that might maintain large the genetic diversity of a species, like pear, and help breeders to cope with climatic changes and the evolving demand of the market. This paper reports the analysis of 170 pear accessions profiled at 12 simple sequence repeat (SSR) markers. The collection was replicated in three different locations and the identification of matching profiles of duplicated genotypes reduced the dataset to 118 genotypes. Of these, 32 (27.1%) were shown to be triploid by flow cytometry, a result that was confirmed by the occurrence of triallelic profiles at molecular markers and the large leaf size. The geographic location of original plants explained very little molecular variance (2%), that was instead very high among genotypes (98%). This evidence confirms the extensive exchange of plant material among the different geographic areas of the region as well as with neighbouring countries as reported in historical documents. The analysis of synonymy revealed 38 duplicated genotypes and reduced the dataset to 80 unique genotypes, of which 12 were triploid (15.0%). The molecular metrics analysed on 70 unique diploid genotypes, including two commercial cultivars, ‘Abate Fetel’ and ‘Conference’ added as controls, revealed that the observed heterozygosity over all loci (Ho) was 0.742 (range 0.471–0.937 for individual loci), while the expected heterozygosity or gene diversity was 0.808 (range 0.534–0.912). The polymorphic information content was 0.784 on average (range 0.501–0.906 for individual loci). The probability of identity (PID) calculated for individual loci and unrelated genotypes ranged from 0.014 for the most discriminating locus, Ch01d09, to 0.250 for the least discriminating one, Ch04e03. The PID product over all loci was 2.50e−16 for unrelated genotypes and 4.86e−06 for full sibs. The analysis of data is integrated with a discussion on the use of SSR markers in pear genotyping and the origin and the frequency of triploids compared with data from the literature. Finally, a discussion on the resemblance of several groups of cultivars to those of the pomological treatises is included.