- European hazelnut, an important nut crop in Oregon agriculture, is threatened by the fungal disease eastern filbert blight (EFB) caused by Anisogramma anomala (Peck) E. Müller. The hazelnut breeding program at OSU has been working on development of EFB-resistant cultivars. DNA markers allow mapping of traits using segregating progenies and identification of linked markers. The breeding of hazelnuts involves use of DNA markers to genotype individuals and facilitate selection in a procedure known as marker-assisted selection (MAS). This technique is particularly promising in tree crops with a long juvenile phase like the hazelnuts. 'Gasaway' resistance governed by a dominant allele at a single locus was identified and several EFB-resistant cultivars carrying the dominant allele from this source have been released. Infection of 'Gasaway' and some of its offspring by A. anomala isolates has
been noted, and indicates an urgent need to investigate new sources of resistance, identify new resistance genes and incorporate them into the breeding effort.
New microsatellite markers were developed from the genomic sequence of hazelnut cv. 'Jefferson'. A total of 17,802 simple sequence repeat (SSR) motifs exceeding 15 bp in length and consisting of tri-, tetra-, penta- and hexa- nucleotide repeats were identified in the 'Jefferson' genome. Removal of duplicates, short fragments, repeats at ends, and repeats containing only A's and T's reduced the number of unique fragments to 2,069. Visual inspection of these unique fragments alligned with genome sequences of 7 other accessions in Tablet software identified 489 sequences with variation in number of repeats but with conserved flanking regions. Amplification of a set of 24 diverse accessions and separation on agarose gels led to the development of 366 new polymorphic markers. These were used to genotype 48 diverse accessions using capillary electrophoresis for fragment sizing. An additional 15 parents were also fingerprinted at these new 366 microsatellite loci. Using the mapping population (OSU 252.146 x OSU 414.062), 213 loci were mapped. A dendrogram was constructed which showed a high level of polymorphism in hazelnut.
Tightly linked markers were identified for 'Gasaway' resistance and MAS is routinely used. The hazelnut acreage in Oregon is increasing every year with the planting of these new EFB-resistant cultivars. However, concern about disease resistance breakdown prompted an investigation of 12 new EFB resistance sources. Segregating progenies were inoculated by placement of potted trees under an
inoculation structure, in the greenhouse, or in the field by tying a diseased branch on each tree. A chi-square goodness-of-fit test was used compare observed with expected segregation ratios. Very few seedlings of Moscow selections N01, N01-06, and N01-07 were resistant and were likely escapes. 'Grand Traverse', C. heterophylla 'Ogyoo', 'Yoder #5', C. americana 'Rush', Moscow N23, N26, N27, and N37 segregated in 1:1 ratio, indicating resistance governed by a single locus and a dominant allele for resistance. 'Uebov' transmitted resistance to only ~15 % of its seedlings. Resistance from 'Uebov', 'Grand Traverse', and C. heterophylla 'Ogyoo' were assigned to LG6 but only 'Uebov' and 'Grand Traverse' were mapped. Resistance from 'Yoder #5', Moscow N27 and C. americana 'Rush' was assigned to LG7. Mapping of the remaining resistance sources will be completed in the future.