Genotyping apple (Malus x domestica Borkh) heirloom germplasm collected and maintained by the Regional Administration of Friuli Venezia Giulia (Italy)

This paper reports the genetic diversity of apple germplasm collected in the Friuli Venezia Giulia region (Italy). The collection, maintained in three different locations, was represented by local varieties likely originated as chance seedlings admixed with varieties introduced since centuries from neighbour countries, for most of which the name and origin was lost with the time. A preliminary procedure described in the paper started from 469 molecular profiles analysed at 15 Simple Sequence Repeat (SSR) markers and allowed to identify the ‘true-to-type’ genotypes among those maintained in multiple locations. The set of the remaining 233 accessions was further reduced to 133 unique profiles by removing 100 synonymy. The flow cytometry analysis allowed to identify as much as 55 triploids (41.4%), whose state was confirmed by field observations on leaf size and the occurrence of triallelic profiles at several SSR markers. The remaining 78 diploid accessions were analysed for their genetic diversity, that is the number of alleles, observed and expected heterozygosity, polymorphism information content (PIC), the frequency of null alleles and the probability of identity for unrelated and full-sib genotypes. The paper provides a critical evaluation of the SSR markers adopted for the study, discusses the genetic diversity observed in the apple collection examined as well as the high occurrence of triploids compared with other apple collections described in the literature.