High-Resolution Genetic and Physical Mapping of the Eastern Filbert Blight Resistance Region in 'Jefferson' Hazelnut ( L.).

Eastern filbert blight (EFB), caused by the pyrenomycete (Peck) E. Müller, is a devastating disease of European hazelnut ( L) in the US Pacific Northwest. A dominant allele at a single locus from the obsolete pollenizer 'Gasaway' confers a high level of resistance to EFB. To identify the gene responsible for resistance, we initiated map-based cloning efforts in a population of 1488 seedlings that segregated for resistance. Chromosome walking was initiated using primers designed from eight previously identified random amplified polymorphic DNA markers linked to resistance. The bacterial artificial chromosome (BAC) library was screened using the primer pairs in a polymerase chain reaction-based pooling and subpooling strategy. Here, we report construction of a high-resolution genetic map and a physical map of the resistance region. Further, we sequenced BACs in the resistance region and identified and annotated the coding sequences. In seven contigs <1 cM from the resistance locus, 233 genes were predicted. The putative genes were compared with sequences in GenBank using a BLASTP search. Fifty-one markers were placed on the high-resolution genetic map, including markers newly developed from the BACs. Segregation in the mapping population placed the resistance locus in a single contig of three BACs (43F13, 66C22, and 85B7). Two of the putative genes are in the p-loop NTPase and F-box super-families localized in a 135-kb BAC, which have previously been shown to have disease-resistance properties. Further mapping, complementation, and expression tests of the genes in these BACs is essential to confirm which confer resistance to EFB.