Genomic Tools Enhance Power and Precision of Hazelnut Breeding

European hazelnut (Corulus avellana L.) is the only economically important nut crop in the family Betulaceae.  Because of its small genome size (~ 385 Mb/1C), relatively short life cycle, availability of a dense linkage map, and amenability to transformation by Agrobacterium, the European hazelnut could serve as a model plant for the Betulaceae.  Genomic resources are being developed and used in the hazelnut breeding program at Oregon State University (OSU) to develop new cultivars that combine suitability to the blanched kernel market with resistance to eastern filbert blight (EFB) caused by the ascomycete Anisogramma anomala (Peck) E. Müller.  Genetic resistance to EFB was first identified in the obsolete pollinizer ‘Gasaway’, and most advanced selections carry this resistance.  Greenhouse inoculations revealed a high level of resistance in eight cultivars and 15 numbered selections.  We identified DNA markers linked to resistance from different sources and assigned them to linkage groups.  DNA marker-assisted selection (MAS) has been practiced for resistance from ‘Gasaway’ and ‘Ratoli’.  In order to better understand the mechanism of resistance, map-based cloning of the ‘Gasaway’ resistance gene was initiated by constructing a bacterial artificial chromosomes (BAC) library for ‘Jefferson’, which is heterozygous for resistance.  A high-resolution genetic map of the resistance region was created with 51 markers and the resistance phenotype in a mapping population of 1488 seedlings.  In parallel, a physical map was constructed.  The BACs in this region were sequenced using Illumina technology and the resistance region was identified as a single contig of three overlapping BACs.  Ab initio gene annotation of the sequence information revealed five candidate genes, two of which are reported to have disease resistance properties.  Further, a set of 24 simple sequence repeat (SSR) markers were developed from sequences in the resistance region and used to characterize 50 diverse hazelnut accessions.  ‘Jefferson’ hazelnut transcriptome sequences (Todd Mockler, OSU) are being used to develop new SSRs.  Future studies will focus on the S-locus which controls sporophytic incompatibility, and gene expression in styles and pollen.