INTRODUCTION
The genus Castanea is divided taxonomically into 13 species and is naturally spread in three major geographical areas: Europe, where the European species (Castanea sativa Mill.) is cultivated for nuts and wood; Asia, where Castanea crenata Sieb. and Zucc. is grown in Japan and C. mollissima B.L. in China and Korea; North America from where Castanea dentata Borkh originates, a giant wood tree, which dominated in the broadleaf forests to the East of the Continent. In the early twentieth century the American chestnut was almost totally destroyed by canker blight (Cryphonectria parasitica).
The genus has great genetic diversity and suitable traits for breeding (size, ease of peeling, no pellicle intrusion, sweetness, flavour and texture of nuts) are present in one or more of the many species. The chestnut ideotype is a function of the final use of nuts or timber and of production technology (harvesting systems, fresh or processed use). However, objectives such as ease of propagation and resistance to major diseases and pests are essential to the establishment of the chestnut industry.
Breeding may allow for the selection of new and better cultivars, with improved timber or nut quality, higher production, easier propagation (rooting of cuttings and layers, no graft incompatibility barriers) mechanical harvesting capabilities (dehiscent or non-dehishent burrs), storage characteristics, disease and pest resistance (Phytophthora cambivora and P. cinnamomi, Cryphonectria, weevils, gall wasp). Interspecific crosses are possible and many hybrids are already in orchard cultivation.
Genes of resistance to Phytophthora and Cryphonectria are found in C. crenata and in C. mollissima. Large nut size, sweeter flavour, good texture and no pellicle intrusion are found in C. sativa marrone genotype. The nuts of C. mollissima have a good weight (10-30 g), no pellicle intrusion and a thin and easily removable pellicle. Early bearing, early ripening and small tree size are found in C. crenata. The C. dentata species has a fast, straight growth with strong central leader but is extremely susceptible to canker blight.
Although hybridization work began a long time ago, only very recently have breeding, based on knowledge of genetics and inheritance of important characters, and selection, based on modern techniques (rapid screening, marker genes, DNA mapping, backcross and recurrent selection) been possible.
