The 2012 ASHS Annual Conference

Eastern filbert blight (EFB), the fungal disease caused by the pyrenomycete Anisogramma anomala (Peck) E. Müller, is a significant disease of European hazelnut (Corylus avellana L.) in the U.S. Pacific Northwest.  Disease progress can be slowed by cultural practices and fungicide applications, but the disease significantly reduces productivity of infected trees and leads eventually to premature death.  Genes conferring qualitative resistance (R genes) to EFB have been discovered and utilized in breeding to confer high levels of resistance to progeny.  Accessions such as ‘Gasaway’, ‘Ratoli’ and OSU 408.040 have been used to introgress resistance into advanced selections.  The cultivars ‘Yamhill’, ‘Santiam’, and ‘Jefferson’, developed by Oregon State University (OSU), have high levels of resistance conferred by a dominant allele from ‘Gasaway’.  There is concern that a single dominant gene resistance may break down under disease pressure, so it is desirable to identify novel sources of resistance and use them in breeding, eventually in gene pyramiding.  Two hazelnut accessions, 'Culpla' (Spanish origin) and OSU 495.072 (Russian origin), have shown resistance to EFB.  When crossed with susceptible selections, the progeny show a 1:1 segregation for resistance, indicating that each resistance is conferred by a dominant allele at a single locus.  Two segregating seedling populations (OSU 675.028 x 'Culpla' and OSU 713.068 x OSU 495.072) were used to map the resistance genes.  Greenhouse and outdoor structure inoculations were used to obtain a disease phenotype for individuals in the populations.  Correlation of disease phenotype with simple sequence repeat (SSR) marker alleles indicates that resistance in both populations maps to linkage group 6.  All known SSR markers from linkage group 6 were used to fingerprint the seedlings and map the resistance loci.  The maps show that the resistance from 'Culpla' and OSU 495.072 is in the same region as ‘Gasaway’ resistance, and may represent a cluster of R genes.  SSR markers linked to EFB resistance from these sources will be useful for introgressing resistance in the hazelnut breeding program.