2005 Annual Report 4d.Progress report. This report serves to document research conducted under a specific cooperative agreement between ARS and Oregon State University. Additional details of research can be found in the report for the parent project 5358-22000-030-00D Biology and Control of Foliar and Fruit Diseases of Horticultural Crops. S. Mehlenbacher and cooperators distributed scions of selections from their breeding program to nurseries that are currently propagating and evaluating selections with the eastern filbert blight (EFB) resistance allele from 'Gasaway' and desirable nut characteristics, precocity and yield. EFB-immune selection OSU 509.064 was released as new cultivar 'Santiam' in February, 2005. EFB-immune selection OSU 553.090 is a candidate for release in 2006. In vitro cultures were established of several promising selections, which are also being evaluated for horticultural characteristics in replicated trials. The release notice for four EFB-immune pollinizers ('Gamma', 'Delta', 'Epsilon' and 'Zeta) was published in HortScience (39:1498-1499). Fourteen hundred primers were screened to identify 35 RAPD markers linked to the 'Gasaway' allele, and the results published in Theoretical and Applied Genetics (108:651-656). Two RAPD markers were used to screen 3000 seedlings for resistance. A preliminary linkage map was constructed for hazelnut, presented at the Sixth International Congress on Hazelnut in June 2004, and will be published in Acta Horticulturae. A more complete linkage map that includes 30 SSR markers has been accepted for publication in Genome. To date, breeding efforts for resistance to EFB have focused on the 'Gasaway' allele, but other sources of resistance are needed to ensure durable resistance to this disease. 'Zimmerman' appears to have the same resistance gene as 'Gasaway', as the same RAPD markers are useful for both sources. Alleles at 21 SSR loci indicate that 'Zimmerman' originated from a cross of 'Barcelona' and 'Gasaway'. S. Mehlenbacher and cooperators have identified additional resistant genotypes of European hazelnut, including OSU 408.040, 'Ratoli', a cultivar from the Republic of Georgia (Georgian 759.007), and a seedling from southern Russia (OSU 495.072). All have been used as parents in crosses with susceptible selections. In such crosses, resistance in OSU 408.040 and 'Ratoli' is transmitted to half of their offspring, indicating control by a single locus. AFLP markers were identified for the dominant resistance allele from 'OSU 408.040' and the results published in the Journal of the American Society for Horticultural Science (130:412-417). The resistance in 'Georgian 759.007' and 'Russian 495.072' was found to be transmitted to about 2/3 of the seedlings. A search for RAPD markers linked to resistance from these sources was recently initiated. S. Mehlenbacher and cooperators identified additional accessions with complete resistance. Greenhouse tests showed that 'Culpla' from Spain and COR 187 from Finland were completely resistant. Exposure of potted trees under structures topped with diseased wood showed that three additional cultivars remained free of disease: one cultivar ('Lozovskoi Sharovidnii') from Kharkiv, Ukraine and two cultivars ('Uebov' and 'Crvejne 3/96') from Cacak, Serbia. Quantitative resistance to the disease is being characterized. Promising selection OSU 540.130 combines a high level of quantitative resistance (comparable to 'Tonda di Giffoni') with high yields and excellent kernel quality, and is a candidate for release in 2006. Multiple sources of resistance identified through this research will be useful in breeding cultivars of hazelnut with durable resistance to EFB.