Biochemical, metabolic and molecular characterization of pear-apple hybrids: PEARAPPLE-Omics

Apple and pear are economically important fruit crops well known for their unique textures, flavours and nutritional qualities. Both genera are characterised by a specific pattern of secondary metabolites, which directly affect not only the resistance or susceptibility towards certain diseases, but also have a significant impact on flavour and nutritional value of the fruits. The similar chromosome number, genome size, and their recent divergence date, together with DNA-markers have shown that apple and pear genomes are highly co-linear. Since hybrids between apple and pear provide a unique germplasm resource for genomic, transcriptomic and metabolic profiling studies, the main task of this project was to understand whether putative apple-pear hybrids available from FEM, PFR and UniBo are true hybrids or not. This research work was in cooperation with the University of Udine. This PhD project utilized comparative genomic approaches; high resolution melting, single nucleotide polymorphism (SNP) analysis, simple sequence repeats and SNP-chip analysis to identify genetic differences among the putative hybrids and its offspring. Furthermore, this work analysed the genus-specific metabolite pattern and the resistance or susceptibility to fire blight, apple scab and pear scab in these plant materials. Another study was to identify candidate genes, involved in the arbutin pathway. The markers analysis and the biochemical analysis demonstrated that the Zwintzscher’s Hybrid and the ‘Abate’ x ‘Fuji’ hybrid are true full hybrids. All PFR F1 progenies are partial hybrids. The hybridity of P26A19 4 and the F2 hybrid F2-FP12 1-1.2-OP were confirmed with the chemical analysis. The UniBO accessions ‘Decana’ x ‘Murray’ 1 and ‘Decana’ x ‘Murray’ 2 are not hybrids, but only have pear genomes. Almost all the ‘Fuji’ progenies were susceptible and, in our work, were moderately susceptible or susceptible to fire blight. CO, P26A19, IP26, IP12, FP12 3 and three FP35 seems to be resistant to apple scab, but all the PFR F1 progenies were resistant to V. pyrina. CO population and P26A19 4 pear x apple hybrids exhibited low to no fire blight infection. The ‘Imperial Gala’ progeny, P26A19 3 and P26A17 are susceptible to fire blight. Three candidate genes involved in the arbutin pathway, 4CL, HBS and CPL, were differentially expressed in pear and apple-pear, as compared to apple. Future work can use the true and partially hybrids to introduce more traits of interest, such as, e.g., flavour or texture in apple or pear and to understand better the arbutin pathway.