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ADDITIONAL INDEX WORDS. Corylus avellana, Anisogramma anomala, microsatellite, simple sequence repeat, linkage map ABSTRACT. European hazelnut (Corylus avellana L.) is a significant crop in Oregon, where 99% of United States hazelnuts are produced. Eastern filbert blight (EFB) caused by Anisogramma anomala (Peck) E. Mü ller is an important disease that infects the trees, reduces yield, and causes premature death. Managing the disease through cultural methods and fungicide applications is laborious and expensive, and genetic host resistance is considered the most viable option for control. Genetic resistance from 'Gasaway' has been used to develop resistant cultivars including Yamhill and Jefferson, but concern about the durability of this single resistance gene stimulated a search for additional sources of resistance. This study used three recently identified sources of EFB resistance: 'Culpl a' from Spain, 'Crvenje' from Serbia, and OSU 495.072 from southern Russia. RAPD markers linked to resistance from 'Gasaway' were absent in all three accessions. Disease response was noted in segregating progenies following greenhouse or structure inoculation, and the resistance loci were mapped using microsatellite markers. In only four of the nine progenies did segregation for disease response fit the ratio of 1 resistant:1 susceptible expected for a single locus, a heterozygous resistant parent, and a dominant allele for resistance. Three progenies showed an excess of resistant seedlings while two showed a deficiency of resistant seedlings. The reciprocal translocations reported in several leading hazelnut cultivars may be present in the parents of the studied progenies, and affecting the segregation ratios. Microsatellite marker A614, previously mapped to linkage group (LG) 6, was closely linked to resistance from all three sources. Maps were constructed for LG6 for each resistant parent using microsatellite markers. The three resistance loci mapped to the same region on LG6 where resistance from 'Gasaway' and OSU 408.040 are located. The resistance alleles in all five accessions may be the same, or more likely are a cluster of different resistance genes in the same region. Markers LG628, LG610, and LG696 will be useful to breed new hazelnut cultivars with resistance from Culpl a, Crvenje, and OSU 495.072.

Pollen–stigma incompatibility in european hazelnut (Corylus avellana L.) is of the sporophytic type and under the control of a single locus with multiple alleles (haplotypes). The S-locus was previously assigned to linkage group 5 (LG5) and linked DNA markers were identified. The loci that control leaf color and style color are linked to the S-locus. We investigated segregation for leaf and style color and S-alleles in two progenies, mapped the loci, and compared the two new maps with the LG5 reference map using simple sequence repeat (SSR) markers. Segregation for color, S-alleles and SSR markers fit expectations. The color loci and the S-locus mapped to LG5 between SSR markers B028 and B774. The three maps aligned and the SSR markers were collinear. The SSR markers closest to the S-locus are KG819, KG847, and BR259. In progeny 05050, which segregated for style and leaf color, no recombination was observed between the two traits. Recombination between the S-locus and the style color locus was 5.4 cM in progeny 05050 and 10.1 cM in progeny 00064. The style color locus was placed very close to SSR marker B028 in both progenies. On the reference map, random amplified polymorphic DNA (RAPD) markers 564-500M, 345-1050dF, and 204-950dF and intersequence simple sequence repeat (ISSR) marker 815-540dF are very close to the S-locus. The identification of closely linked markers will facilitate the map-based cloning of the S-locus and color loci in hazelnut.