Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2005
Publication Date: 2/20/2006
Citation: Mehlenbacher, S., Brown, R., Nouhra, E., Gokirmak, T., Bassil, N.V., Kubisiak, T. 2006. A genetic linkage map for hazelnut (corylus avellana l.) based on rapd and ssr markers. Genome. 49:122-133.
Interpretive Summary: DNA markers serve as genetic landmarks and are interspersed among the genes throughout the chromosomes of hazelnut. If a marker is located near a gene of interest, the marker can be used to identify the desired form of the gene. For example, the hazelnut breeder can use a DNA marker to identify plants that carry the form of the gene that gives resistance to eastern filbert blight. This disease is of great concern to the hazelnut growers in the Pacific Northwestern United States. Linkage maps identify blocks of markers and genes that are closely associated. Ideally, each linkage group corresponds to a chromosome. Linkage groups are important because they help in identifying the location of genes of interest. In this research, we used two types of DNA markers (RAPDs and SSRs) to create a linkage map of the hazelnut in a seedling population of 144 individuals that are segregating for resistance to eastern filbert blight. The maps of each parent were grouped into eleven expected groups. The resistance gene was placed on group 6 of the maternal map. A gene responsible for successful pollination between the male and the female parent was placed on group 5 of the paternal map. Placing SSR markers on this map will make it useful in other hazelnut populations. The addition of more markers to the map will assist in locating and isolating useful genes for use in hazelnut breeding.
Technical Abstract: A linkage map for European hazelnut (Corylus avellana L.) was constructed using random amplified polymorphic DNA (RAPD) and simple sequence repeat (SSR) markers and the 2-way pseudotestcross approach. RAPD markers in testcross configuration segregating 1:1, were used to construct maps for each parent. Fifty additional RAPD loci were assigned to linkage groups as accessory markers whose exact location could not be determined. Markers in intercross configuration, segregating 3:1, were used to pair groups in one parent with their homologues in the other. Eleven groups were identified for each parent, corresponding to the haploid chromosome number of hazelnut (n = x = 11). Thirty of the 31 SSR loci were able to be assigned to a linkage group. The maternal map included 249 RAPD and 20 SSR markers and spanned a distance of 661 cM. The paternal map included 271 RAPD and 28 SSR markers and spanned a distance of 812 cM. The maps were quite dense, with an average of 2.6 cM between adjacent markers. The S-locus, which controls pollen-stigma incompatibility, was placed on chromosome 5S where 6 markers linked within a distance of 10 cM were identified. A locus for resistance to eastern filbert blight, caused by Anisogramma anomala, was placed on chromosome 6R for which two additional markers tightly linked to the dominant allele were identified and sequenced. These maps will serve as a starting point for future studies of the hazelnut genome, including map-based cloning of important genes. The inclusion of SSR loci on the map will make it useful in other populations.