Interspecific hybridization of chestnut
Résumé
Chestnut (Castanea) is a tree genus distributed throughout the northern Hemisphere in natural stands, orchards, and coppices. As a multipurpose tree, chestnut is used to produce timber, nuts, tannins, and other related products. Interspecific hybridization was first done in 1894 in the USA, in the 1910s in Japan, and in the 1920s in Europe. In the USA, blight resistant Chinese (C. mollissima) and Japanese (C. crenata) species have been used since 1930 as the pollen parents in a backcrossing program with American chestnuts (C. dentata) as the recurrent parent, in order to produced blight resistant timber chestnuts. In Europe, Japanese chestnut trees were introduced because of their resistance to ink disease (caused by Phytophthora spp.). A clonal collection of hybrids of Japanese chestnut crossed with European chestnut (C. sativa) is used to produce nuts and timber, and for rootstocks for local cultivars. The pellicle of the Japanese chestnut cultivars is not easily removed, but this has been overcome with the newly released Japanese chestnut hybrid ‘Porotan’, with the easy-peel pellicle trait controlled by a single recessive gene (P/p) from native Japanese chestnuts. After more than 100 years of chestnut hybridisation, new technologies and the recently reported genome sequence will allow us to face new threats and to maintain the rich genetic and cultural heritage of chestnut.