Development of a genetic linkage map for molecular breeding of chestnut

In the last 50 years the nut production of Castanea sativa in Europe has strongly declined due to various factors: the aging of the population in the areas of growing, changes in the structure of society, and the spread of diseases and pests, including the chestnut gall wasp (Dryocosmus kuriphilus, Yasumatsu). Yet, recently, the interest for the planting of new and modern orchards has grown in many areas of Europe and there is an increasing demand for cultivars and rootstocks more tolerant to biotic factors and adapted to the changing climate. The spread of the gall wasp in Italy has promoted breeding strategies and studies on resistance to the insect. In this frame the Castanea sativa cultivar ‘Madonna’ and the Eurojapanese hybrid ‘Bouche de Bétizac’ (C. sativa x C. crenata), susceptible and resistant to gall wasp respectively, were used to create progenies for selecting new cultivars, investigating the mechanism of resistance to the cynipid and studying agronomical and technological traits. A progeny of 250 plants segregating for resistance to the pest and for phenological, morphological and nut traits were obtained. One hundred and forty eight plants of the progeny, currently 8 years old, were analysed at 132 SSR loci, and for agronomic traits such as time of budburst, tree habit, and resistance to D. kuriphilus. Data were statistically analysed to obtain two genetic linkage maps and identify putative QTL regions and markers associated to the resistance trait. This work represents an initial step in the identification of chromosomal regions carrying genes of interest, useful for breeding programs and to develop marker-assisted selection.