Abstract:
Eastern filbert blight, caused by Anisogramma anomala (Peck) E. Muller,
is a serious threat to hazelnut (Corylus avellana L.) production. Resistant
cultivars offer the best control. Screening systems were needed to reliably
identify disease, particularly in immune progeny derived from 'Gasaway'. An
indirect enzyme-linked immunosorbant assay (ELISA) was developed using
polyclonal antibodies obtained from rabbits injected with A. anomala. One-thousand-
fold dilutions of the antiserum produced a positive reaction to a 1.7 x
10⁶ dilution of extracts from infected hazelnut but did not react to healthy plants.
ELISA was more sensitive and efficient than microscopic detection.
Two methods of screening hazelnut for quantitative resistance to eastern
filbert blight were compared for their ability to differentiate between genotypes
and for correlations between the two protocols. One method utilized a field plot
in a randomized block design with inoculated trees planted in the borders as the
disease source. The second method was based on exposing three sets of potted
clones to high doses of inoculum in 1990 (Pinkerton et al., 1993), 1992-93, and
1993. Disease incidence and proportion of wood cankered as determined by the
two methods were significantly correlated in each year of the study. A map of
the field plot disease incidence indicates that the inoculum was present throughout
the blocks.
Additional sources of resistance are desirable. Seedlings of 'Gem' were
all susceptible and seedlings of 'Zimmerman' segregated for resistance following
greenhouse inoculation. The immunity of 'Gasaway' was confirmed as being
conferred by a single dominant gene. Of the species material, clones of C.
cornuta var. californica, C. heterophylla, and C. sieboldiana, most C. americana
and one C. colurna clone were resistant, as were seedlings of C. cornuta var.
cornuta and C americana. C. jacquemontii seedlings were highly susceptible, as
were two suspected C. colurna x C avellana hybrids. Five C. americana x C.
avellana hybrids were highly resistant. One of C. cornuta var. californica x C.
avellana and two of the C. heterophylla x C. avellana hybrids were resistant.
These sources of resistance are being used to broaden the genetic base of the
breeding program.
