Linkage maps development and biotechnological tools for hazelnut and chestnut breeding

The cultivation of nut species, such as hazelnut and chestnut, still largely relies on traditional cultivars that were selected across centuries. Up to date, only a few breeding programs are active, yielding a limited number of new accessions, due to the particularly long time required for the selection process and the high heterozygosity of these species. There is an urgent need for improved breeding techniques based on marker-assisted selection (MAS) and biotechnological tools, to face new threats, such as the spread of alien species and the climatic changes. In this research we present the results of 10 years of activity addressed to the development of genetic maps in hazelnut (Corylus avellana L., progeny 'Tonda Gentile delle Langhe' × 'Merveille de Bollwiller' syn. 'Hall's Giant') and chestnut (progeny Castanea sativa × (C. sativa × C. crenata)) aimed at the detection of markers putatively useful for MAS. Saturated maps for the parent cultivars of the two progenies, accounting about 180 individuals each, were constructed using both SSR markers and SNP markers obtained by genotyping by sequencing, using the reference genomes as template. In hazelnut, phenological traits and fruit characters of commercial and technological relevance were mapped as QTLs; in chestnut, a trait of resistance to Dryocosmus kuriphilus Yasumatsu was mapped as a simple Mendelian character, and its genomic region is under deep investigation to find putative genes of resistance. Further breeding strategies are being carried out for hazelnut using in vitro techniques aimed at developing efficient systems of genetic transformation and regeneration for the modification or introduction of genes, such as those related to self-incompatibility and resistance to major pathogens.