Chestnut Breeding in the United States for Disease and Insect Resistance

The genus Castanea (family Fagaceae) is found in north temperate climates around the world, and is highly prized in many different cultures for its nutritious nuts and valuable timber. Selection for larger, better-tasting nuts has been ongoing in Asia and Europe for centuries. Early trade routes moved European chestnut trees (C. sativa) west of their native range (in the Caucasus mountains), and the Romans then moved them across their empire to provide support posts for grapevines, as well as for the nuts. Cultivar selection in Turkey, Italy, Spain, and Portugal has been extensive, and regional favorites developed. The many uses of the wood of American chestnut made this "all purpose" tree extremely valuable in its native range in North America. Nut production was important as a food source for rural families and many species of birds and animals. The other American species in the genus Castanea are classed as chinquapins, and may be divided into several or lumped as a single species. The small nuts from these trees and bushes serve primarily as mast for wildlife. Two serious diseases of chestnut trees changed the direction of chestnut research in the United States. Ink disease, caused by the root pathogen Phytophthora cinnamomi, was discovered to be the cause of widespread death of chestnuts and chinquapins in the southern United States, which had been observed since about 1850. This imported pathogen probably came into the southern United States before 1824. The second chestnut disaster was the introduction of chestnut blight disease, which was first found in the United States in 1904. The pathogen causing the lethal cankers is an Ascomycete now known as Cryphonectria parasitica. The longest continuing chestnut breeding program in the United States is in Connecticut.