Characterizing the response of diverse hazelnut germplasm to eastern filbert blight in New Jersey
Creators: name: Jacobs, Daniel C.
Publisher: name: No Publisher Supplied
Year: 2024

description: The fungal disease eastern filbert blight (EFB), caused by Anisogramma anomala, is the primary limiting factor to European hazelnut (Corylus avellana) production in the United States. Developing resistant cultivars is considered the most effective management strategy. Breeding efforts at Oregon State University (OSU) have successfully introgressed the dominant EFB resistance gene (R-gene) from ‘Gasaway’ into commercial quality cultivars that have been widely adopted in the Willamette Valley of Oregon, where &gt;99% of US hazelnut production occurs. Concerns over the durability of a single gene for resistance drove germplasm screening efforts at OSU and instigated germplasm collection trips throughout the native range of C. avellana by OSU and Rutgers University, which resulted in the identification of over 100 sources of resistance to EFB. Sources exhibit tolerance (quantitative resistance [QR]) or qualitative resistance associated with R-genes, 34 of which have been mapped to three of C. avellana’s eleven genetic linkage groups (LGs). However, A. anomala exhibits pathogenic variation between populations and some selections made at OSU, where the pathogen is believed to be genetically uniform, have shown variable resistance expression when exposed to A. anomala populations in New Jersey, including trees protected by the ‘Gasaway’ R-gene. Further variability has been observed in long term disease trials at Rutgers, where mature, previously resistant trees started expressing EFB, in some cases more than 15 years after initial exposure to A. anomala. The goals of these studies were to identify changes in resistance expression in Rutgers’ foreign germplasm introductions (n=154) and to characterize differences in EFB resistance expression in cultivars and breeding selections deemed resistant or highly tolerant to EFB at OSU (n=106) when planted in replicated trials at Rutgers. In the germplasm collection, we found 91 introductions that remain resistant, representing only 1.7% of the original 5,226 seedlings planted at Rutgers. New infections (n=63) were severe and primarily linked to trees in specific seedlots, indicative of a breakdown in resistance. The 91 remaining foreign introductions represent 54 distinct seedlots from 7 countries and span 14 of 18 resolved C. avellana genetic clades. Similarly, the 106 cultivars and breeding selections from OSU exhibited variable response to A. anomala at Rutgers. With only two exceptions, cultivars/selections carrying resistance mapped to LG6 (n=30), including the ‘Gasaway’ R-gene, exhibited severe EFB with canopy death observed in 232 of 266 (87%) individual trees. In addition, EFB was identified on carriers of R-genes mapped to LG7, with ‘Ratoli’ related selections (n=4) developing EFB for the first time in their over 20 years of observation at Rutgers, although all other LG7 protected selections (n=7) showed no signs of EFB. With one exception, selections mapped to LG2 (n=9) showed no EFB and cultivars/selections expressing QR (n=50) exhibited disease phenotypes more similar to what they expressed at OSU. These collective findings support that A. anomala displays pathogenic variation between populations and that long term observation of resistance sources across multiple locations and pathogen populations is needed to select durable forms of resistance. Fortunately, dozens of genotypes still exhibit useful levels of resistance/tolerance at Rutgers and constitute a diverse base from which to develop cultivars with sustainable resistance to EFB.