Chestnut (Castanea spp. Miller) Breeding

The chestnuts and chinquapins are a group of about seven species of trees and shrubs in the genus Castanea. They are of considerable importance ecologically in all the areas of their natural occurrence, and the chestnuts especially are of great economic value for their lumber and for their nut crop wherever they are cultivated. Two catastrophic diseases, chestnut blight caused by the ascomycete fungus Cryphonectria parasitica (Murr.) Barr and Phytophthora root rot (ink disease) caused primarily by the soil-borne oomycetes Phytophthora cinnamomi Rands and P. cambivora (Petri) Buisman, have severely impacted chestnut in Europe and North America. Therefore, much of the breeding work continues to focus on breeding for resistance to these two diseases. The most serious insect pest of Castanea is the Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu. Variation in host tolerance to D. kuriphilus has led to development of new gall-resistant chestnut cultivars. Interspecific hybridization offers great opportunity to combine the most favorable traits found in the ample genetic diversity of the genus through introgression into locally-adapted populations. Chestnut breeders in eastern Asia have made great strides towards improvement of chestnut fruit quality and crop yields, and researchers in all chestnut growing regions have made gains in disease resistance by using molecular markers and other genomic tools to assist selection. Biotechnologies that include transmissible hypovirulence as a biocontrol for chestnut blight, tissue culture and other micropropagation techniques, and genetic engineering and transformation technologies are complementary to classical plant breeding programs.