The 2012 ASHS Annual Conference

Fire blight, caused by Erwinia amylovora, is a major threat to apple and pear production world-wide.  To identify genomic regions conferring resistance to fire blight in apple, we searched and identified Single Nucleotide Polymorphisms (SNPs) from publicly available apple EST database, and custom-synthesized a 1536 GoldenGate™ SNP genotyping assay (Khan et al. 2012).  SNPs were genotyped using an apple mapping population consisting of 90 F1 individuals derived from a cross between Co-op 16 x Co-op 17.  A total of 583 SNPs segregated in the mapping population, and these were used to construct a linkage map.  A well-saturated consensus genetic map for both parents using the Haldane’s mapping function was constructed.   The genetic map consisted of 17 linkage groups with an average of 34 ± 6 markers per linkage group.  Overall, the average interval between markers was 2 ± 4 cM.   In addition, progeny of this mapping population was grafted onto Bud-9 rootstock, grown in the greenhouse, and artificially inoculated the with a suspension culture of E. amylovora.  Lengths of necrotic shoots were measured, and percent infected shoots was calculated.  These data were used for QTL mapping together with the newly constructed apple genetic linkage map.  We identified a QTL with moderate effects on one of the linkage groups, and explaining 13-17.5 % of the observed phenotypic variation. The marker is an EST-based SNP with an LOD of ~4.  This interval is being investigated to identify underlying candidates genes associated with fire blight resistance.