Abstract:
To identify novel host genetic resistance to eastern filbert blight, caused by
the fungus Anisogramma anomala (Peck) E. Muller, ninety European hazelnut
{Corylus avellana L.) varieties and interspecific hybrids (with C. americana Marsh,
or C. colurna L.) were screened for response to the eastern filbert blight pathogen
after inoculation in a severe greenhouse test. Six varieties were discovered which
did not display signs of the pathogen or symptoms of eastern filbert blight: 'Closca
Molla', 'Ratoli', 'Yoder #5', 'Potomac', 'Medium Long', and 'Grand Traverse'.
Two of these, 'Ratoli' and 'Closca Molla', are minor varieties from Spain and are
superior agronomic types to 'Gasaway' which is the principle source of resistance
currently being used in the Oregon State University (OSU) breeding program.
Further studies are required to ascertain if the genetics of resistance in these newly
evaluated varieties is unique. None of the six varieties has the UBC 152₈₀₀ RAPD
marker that segregates with the resistance gene found in 'Gasaway'.
Inheritance of resistance to eastern filbert blight also was investigated in
'Zimmerman', a volunteer seedling that was found in 1989 displaying no disease
symptoms despite its proximity to a orchard heavily infested with eastern filbert
blight. Three progenies were created using 'Zimmerman' as the pollen parent in
controlled crosses with three susceptible advanced selections from the OSU
breeding program. The 'Zimmerman' progenies were grown from seed, grafted and
subjected to the same severe inoculation as for the germplasm survey.
The progenies displayed significant deviation from the 1:1 ratio that would
be expected if 'Zimmerman' was hetero2ygous for the 'Gasaway' gene. Resistant
phenotypes make up about 83% of the populations which indicates that the genetics
of resistance in 'Zimmerman' differs at least partially, from that found in
'Gasaway'. The data were congruent with a 3 resistant :1 susceptible ratio which
suggests 'Zimmerman' may possess a second, independent resistance gene. Yet, a
well-characterized RAPD marker, linked to the resistance gene in 'Gasaway',
segregates with the resistant phenotype in all three progeny populations with very
little recombination (2 %, 4 %, and 6%). These newly found sources of resistance
to eastern filbert blight will aid in the release of resistant cultivars and may increase
the stability of genetic resistance to A. anomala.
