Eastern filbert blight (EFB) disease caused by the fungal pathogen Anisogramma anomala (Peck) E. Müller is a major threat to Oregon’s hazelnut (Corylus avellana) industry. Although cultivars with ‘Gasaway’ resistance have sustained the Oregon hazelnut industry, ‘Jefferson’ and ‘McDonald’ trees protected by a dominant allele for resistance from ‘Gasaway’ have shown small cankers when under high disease pressure for several years. In late 2023, a few orchards in the northern Willamette Valley reported infections on ‘Gasaway’ protected trees with highly aggressive cankers and fully developed stromata, indicating the ability to reproduce on resistant varieties and signaling the breakdown of ‘Gasaway’ resistance in Oregon. The OSU hazelnut breeding program has conducted extensive EFB screening efforts on curated germplasm, and more than 30 sources of EFB resistance have been assigned to a linkage group (LG) using SSR loci and disease score correlation analyses. Fine mapping of the LG7 resistance region using the ‘Ratoli’ and OSU 1166.123 backgrounds with simple sequence repeat (SSR) and PCR allele competitive extension (PACE) SNP genotyping assays narrowed the resistance region. However, gene expression profiling is desired to further elucidate which candidate genes overlap between fine-mapping efforts and gene expression to refine marker development efforts for LG7 resistance. The objective of this study was to identify differentially expressed genes (DEGs) in six hazelnut genotypes (‘Ennis’, OSU 1026.073, OSU 1166.123, OSU 541.147, ‘Ratoli’, and ‘Sacajawea’) at different stages of EFB infection. Layered and grafted trees with ‘McDonald’ rootstocks were grown in 3L pots at the OSU West Greenhouses in Corvallis, OR in spring 2023. Inoculations were conducted in an outdoor container pad and new shoot tips with at least two true leaves were spray inoculated with a spore suspension (1x106 spores·mL-1) until run-off. Apical shoots (2-3 internodes) from four biological replicates were collected at 0, 12, 24, 48, 72, 96, 168, and 240 hours post-inoculation, with the addition of two biological mocks sprayed with deionized water. Total RNA was extracted and sequenced using a BRB-seq library prep for the Illumina NovaSeq X Plus platform. Detailed analyses of differentially expressed genes between susceptible and resistant genotypes during the initial stages of EFB infection will be discussed. The results of this study will provide valuable insights into the molecular resistance of hazelnut to EFB, aid marker development for breeding EFB-resistant cultivars, and facilitate the pyramiding of R-genes in a single clonal selection for more durable resistance.
