Investigation of novel sources of genetic resistance to eastern filbert blight

Graduation date: 1999To identify novel host genetic resistance to eastern filbert blight, caused by\ud the fungus Anisogramma anomala (Peck) E. Muller, ninety European hazelnut\ud {Corylus avellana L.) varieties and interspecific hybrids (with C. americana Marsh,\ud or C. colurna L.) were screened for response to the eastern filbert blight pathogen\ud after inoculation in a severe greenhouse test. Six varieties were discovered which\ud did not display signs of the pathogen or symptoms of eastern filbert blight: 'Closca\ud Molla', 'Ratoli', 'Yoder #5', 'Potomac', 'Medium Long', and 'Grand Traverse'.\ud Two of these, 'Ratoli' and 'Closca Molla', are minor varieties from Spain and are\ud superior agronomic types to 'Gasaway' which is the principle source of resistance\ud currently being used in the Oregon State University (OSU) breeding program.\ud Further studies are required to ascertain if the genetics of resistance in these newly\ud evaluated varieties is unique. None of the six varieties has the UBC 152₈₀₀ RAPD\ud marker that segregates with the resistance gene found in 'Gasaway'.\ud Inheritance of resistance to eastern filbert blight also was investigated in\ud 'Zimmerman', a volunteer seedling that was found in 1989 displaying no disease\ud symptoms despite its proximity to a orchard heavily infested with eastern filbert\ud blight. Three progenies were created using 'Zimmerman' as the pollen parent in\ud controlled crosses with three susceptible advanced selections from the OSU\ud breeding program. The 'Zimmerman' progenies were grown from seed, grafted and\ud subjected to the same severe inoculation as for the germplasm survey.\ud The progenies displayed significant deviation from the 1:1 ratio that would\ud be expected if 'Zimmerman' was hetero2ygous for the 'Gasaway' gene. Resistant\ud phenotypes make up about 83% of the populations which indicates that the genetics\ud of resistance in 'Zimmerman' differs at least partially, from that found in\ud 'Gasaway'. The data were congruent with a 3 resistant :1 susceptible ratio which\ud suggests 'Zimmerman' may possess a second, independent resistance gene. Yet, a\ud well-characterized RAPD marker, linked to the resistance gene in 'Gasaway',\ud segregates with the resistant phenotype in all three progeny populations with very\ud little recombination (2 %, 4 %, and 6%). These newly found sources of resistance\ud to eastern filbert blight will aid in the release of resistant cultivars and may increase\ud the stability of genetic resistance to A. anomala