Development of High-Density Genetic Linkage Maps and Identification of Loci for Chestnut Gall Wasp Resistance in Castanea spp

Castanea sativais an important multipurpose species in Europe for nut and timber production as well as for its role in the landscape and in the forest ecosystem. This species has low tolerance to chestnut gall wasp (Dryocosmus kuriphilusYasumatsu), which is a pest that was accidentally introduced into Europe in early 2000 and devastated forest and orchard trees. Resistance to the gall wasp was found in the hybrid cultivar 'Bouche de Betizac' (C. sativaxC. crenata) and studied by developing genetic linkage maps using a population derived from a cross between 'Bouche de Betizac' and the susceptible cultivar 'Madonna' (C. sativa). The high-density genetic maps were constructed using double-digest restriction site-associated DNA-seq and simple sequence repeat markers. The map of 'Bouche de Betizac' consisted of 1459 loci and spanned 809.6 cM; the map of 'Madonna' consisted of 1089 loci and spanned 753.3 cM. In both maps, 12 linkage groups were identified. A single major QTL was recognized on the 'Bouche de Betizac' map, explaining up to 67-69% of the phenotypic variance of the resistance trait (Rdk1). TheRdk1quantitative trait loci (QTL) region included 11 scaffolds and two candidate genes putatively involved in the resistance response were identified. This study will contribute toC. sativabreeding programs and to the study ofRdk1genes.