- European hazelnut is a significant crop in the Pacific Northwest, and the US ranks
4th internationally for hazelnut production. Production in the Pacific Northwest is
threatened, however, by the disease eastern filbert blight (EFB) caused by the fungus
Anisogramma anomala (Peck) E. Müller. To meet the challenges faced by the hazelnut
industry in Oregon and Washington, the breeding program at Oregon State University has
focused on developing DNA marker technology and producing EFB resistant cultivars.
This study focused on developing new microsatellite markers from hazelnut
transcriptome sequences and on disease resistance from three accessions ('Culpla,' 'Crvenje,' and OSU 495.072) which showed no disease symptoms following a series of
DNA markers have been useful in hazelnut breeding for marker-assisted
selection, construction of genetic linkage maps, cultivar fingerprinting, and phylogeny
studies. Previously developed markers include AFLP, RAPD, ISSR, and microsatellite
(SSR) markers developed from enriched libraries and ISSR fragments. This study utilized
the transcriptome sequence from 'Jefferson' hazelnut to mine for microsatellites, align
with the genomic sequence, design primers, screen for polymorphism, and characterize
and map polymorphic markers. A total of 1432 microsatellites were mined from the
transcriptome sequence, and the most frequently found motifs were AG (35.8%), AT
(13.3%), and AAG (12.7%), and 382 primer pairs were designed. Screening showed that 119 markers were polymorphic, and these were characterized on sets of 50 and 14 accessions. Fifty-three markers that segregated in the mapping population or in three alternate populations were mapped and assigned to linkage groups. A dendrogram showed that accessions clustered mostly according to geographic origin. These results confirm the high level of diversity present in hazelnut, and the markers developed in this study will be useful for further genetics studies in hazelnut.
The three EFB resistant parents 'Culpla,' 'Crvenje,' and OSU 495.072 were subjected to two inoculation treatments: greenhouse inoculations and exposure under an inoculation structure. The accessions remained free of disease after both treatments. Progeny segregating for resistance were produced. The progeny were inoculated either in the greenhouse or under the structure, and disease response recorded for each individual. DNA was extracted from seedlings, and sets of 32 seedlings from each resistant parent were screened with previously mapped markers using PCR and capillary electrophoresis. All three resistance sources were correlated with marker A614, allowing the resistance loci to be assigned to linkage group (LG) 6. The progeny were then screened with all known microsatellite markers on LG 6, and linkage maps constructed of the marker loci and resistance loci. Markers KG821, LG628, and LG696 are especially close to the resistance loci and will be useful for marker-assisted selection. Although these resistance loci are located in the same region of LG 6 as the 'Gasaway' resistance gene, they are different from 'Gasaway,' and markers linked to resistance will be useful for introgressing and pyramiding resistance in new cultivars.