Towards a physical map of the locus conferring resistance against the rosy apple aphid Dysaphis plantaginea from the cultivar ‘Florina’

Cultivated apples (Malus x— domestica) are susceptible to several pests including rosy apple aphid (Dysaphis plantaginea, Passerini) which causes severe economic damages. After the phenotypic characterization of two segregating F1 progenies deriving from the resistant cultivar 'Florina', a single resistance gene (denoted Dp-fl) has been postulated. Dp-fl was mapped at the bottom of linkage group 8 of 'Florina', close to SSR CH01h10. Recently, several Single Nucleotide Polymorphisms (SNPs) located downstream from this SSR have been identified and mapped. The two closest SNP markers flanking the Dp-fl gene have restricted the physical interval containing the resistance gene to approximately 330 kb. In the present work, these two flanking SNPs were used for the screening of a 'Florina' BAC library. The aim of this work was to identify a minimum tiling path of BAC clones spanning the Dp-fl locus to identify the putative candidate genes. So far, the first steps of the screening have been successfully completed and six BAC clones have been identified. Sequencing of the BACs is in progress. Once the full sequence of the Dp-fl region will be completed, important knowledge will be gained for both understanding the functional mechanism underlying the resistance and directly targeting the gene in marker-assisted breeding.