2006 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. Dr. Shawn Mehlenbacher and collaborators conducted the following research towards the agreements objectives: Ddistributed 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. Selection OSU 540.130 with a high level of quantitative resistance to EFB and excellent kernel quality was released as new cultivar 'Sacajawea' in January, 2006. EFB-immune selection OSU 553.090 is a candidate for release in 2007. In vitro cultures were established of several promising selections, which are also being evaluated for horticultural characteristics in replicated trials. Research on 'Zimmerman' resistance (14 years of work) was recently accepted for publication in the Journal of the American Society for Horticultural Science. The completely resistant 'Zimmerman' and 'Gasaway' share a common resistance allele, but 'Zimmerman' transmits resistance to 75% of its seedlings while 'Gasaway' transmits resistance to 50%. Two RAPD markers were used to screen 900 seedlings for resistance. A linkage map that includes 29 SSR markers was published 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. 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), a seedling from southern Russia (OSU 495.072), two cultivars from Serbia ('Uebov' and 'Crvejne 3/96'), and 'Yagli Findiq' from Azerbaijan. 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. 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 is in progress. Fifty-eight hazelnut accessions were evaluated for their response to EFB following greenhouse inoculation using ELISA and visual inspection, and a manuscript accepted for publication in HortScience. Forty-five of these became infected, 12 remained free of infection and one gave inconclusive results. The twelve accessions showing complete resistance were: 'Culpla' from Spain and COR 187 from Finland; C. americana × C. avellana hybrids 'G081S', COR 506 and Weschcke selections TP1, TP2 and TP3; C. colurna × C. avellana hybrids Chinese Trazels Gellatly #6 and #11, Turkish Trazel Gellatly #3 and backcross hybrid 'Lisa', and C. heterophylla var. sutchuensis × C. avellana hybrid 'Estrella #1'. In a second test, exposure of potted trees under structures topped with diseased wood confirmed the complete resistance of 'Santiam', four pollenizers, and 'Ratoli'. However, a few small cankers were observed on 'Closca Molla' from Spain in contrast to the results of earlier greenhouse inoculations. Exposure of potted trees under structures topped with diseased wood was used to quantify susceptibility to EFB. 'Sacajawea', 3 OSU selections, and 7 selections of Turkish origin showed less disease than 'Lewis'. Multiple sources of resistance identified through this research will be useful in breeding cultivars of hazelnut with durable resistance to EFB. S. Mehlenbacher and cooperators have developed more than 100 microsatellite loci in hazelnut. These markers will be useful in assigning resistance loci to linkage groups.