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  • Author or Editor: Kenneth B. Johnson x
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A rapid and reliable assay for screening European hazelnut (Corylus avellana L.) genotypes for quantitative resistance to eastern filbert blight [Anisogramma anomala (Peck) E. Müller] was tested by comparing two methods using the same clones. In the first assay, disease spread was followed for five consecutive years (1992-96) in a field plot planted in 1990. Measured responses included disease incidence (the presence or absence of cankers) and total canker length, quantified as the length of perennially expanding cankers. The second assay consisted of annually exposing replicated sets of 2-year-old, potted trees to artificially high doses of pathogen inoculum and measuring incidence and canker lengths at the end of the next growing season. The potted trees were exposed to inoculum in 1990, 1992, 1993, and 1994. Compared to the field plot, disease incidence and total canker length were higher in all the potted-tree experiments. Nonetheless, disease responses of individual clones in the two screening methods were significantly correlated in some contrasts (rs = 0.97 between 1996 field and 1995 potted trees). However, for a few clones (`Camponica', `Tombul Ghiaghli', and `Tonda di Giffoni'), disease developed slowly in the field plot, but disease incidence on these clones averaged > 30% in most of the potted-tree studies. Disease responses also were significantly correlated among some of the potted-tree experiments (rs = 0.72 for the comparison of 1994 to 1995). Highly susceptible and highly resistant hazelnut clones were identified by both methods. However, the field plot method was superior to the potted-tree method for distinguishing among moderately resistant clones. `Bulgaria XI-8', `Gem', `Camponica', `Tombul Ghiaghli', and `Tonda di Giffoni' were identified as promising sources of quantitative resistance to eastern filbert blight.

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Eastern filbert blight is a serious threat to hazelnut (Corylus avellana) production in the Pacific NW. Susceptible genotypes inoculated with the causal fungus, Anisogramma anomala, require 16 to 28 months of incubation to develop symptoms. A rapid and accurate screening system was needed to identify resistant genotypes in the OSU hazelnut breeding program, particularly in progenies segregating 1:1 for a single dominant resistance gene from the variety `Gasaway'. An indirect enzyme-linked immunosorbant assay (ELISA) system was developed using polyclonal antibodies obtained by injecting New Zealand rabbits with antigens from pure cultures of A. anomala. The antiserum produced a positive reaction to the fungus in 1000-fold dilutions of the extracts from infected hazelnut tissue but did not react to 10-fold dilutions of healthy tissue in indirect ELISA.

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