Confirmation of intergeneric hybrids between apple and pear

Malus and Pyrus are closely related, with highly co-linear genomes. However, the two genera are characterized by many specific differences, including disease resistances, secondary metabolites, fruit texture, flavour and shape. Hence, intergeneric hybrids between apple and pear provide a unique germplasm resource for genomic analysis, the application of advanced breeding strategies, and new cultivar development. We utilized two sources of apple-pear hybrid plants, ’Zwintscher’s hybrid’ (Fischer et al., 2014) and its F2 progeny held at FEM, plus putative apple-pear hybrids developed at PFR. We determined which of the putative apple-pear hybrid genotypes were true hybrids by characterising the genomes for hybridity. We scanned the genomes of 47 putative hybrids with High Resolution Melting analysis (HRM) ‘apple/pear’ primers, developed following bioinformatics analysis, to detect SNP variants unique to the apple or pear genomes, respectively. The initial primer set was optimised in a preliminary screen of DNA samples that included ‘Cox’s Orange Pippin’, ‘Old Home’, ’Zwintscher’s hybrid’, its parents and various mixtures. A set of 39 useful primers distributed along the genome was identified and used to screen the 47 putative hybrids. Results indicated these were true hybrids: 9-15 primers per genotype provided evidence for this. Interestingly, the apple and pear parents did not appear to contribute equally to the genomes of the progenies. Screening with a set of SSRs, as well as a preliminary screen of 6 samples over the 20K SNP array (Bianco et al., 2014) validated these results. We plan to screen all hybrid seedlings with the 9K apple/pear SNP array (Chagné et al., 2012; Montanari et al., 2013) to delineate their chromosomal structure.