Resistance of chestnut trees to Asia chestnut gall wasp
Asian chestnut gall wasp (Dryocosmus kuriphihus) was introduced into Georgia (USA) in 1975 and has been spreading north throughout the range of American chestnut (Castanea dentate). This pest is now present throughout most of Tennessee. In 2003, it was found near Cleveland, Ohio and has been spreading south from there. In 1995, hybrid chestnuts with C. dentate female parents and two Ozark chinquapin x Chinese chestnut male parents (C. ozarkensis x C. mollissima) were planted in North Carolina, where this introduced insect is now naturalized. Of the 93 trees planted, 69 survived four years, and 36 were still surviving after 14 years, the progeny of one male parent had a 67% survival and of the other, 16% survival. Among the survivors, 31 had no wasp galls in 2009 and 4 had 10 or fewer galls. The four female parents (American chestnuts and half-sibs) were assumed to be fully susceptible, so the genes controlling resistance to infestation cannot be cytoplasmic. If resistance is conferred by one or two nuclear genes, resistance can easily be transferred into timber chestnuts and orchard chestnut cultivars.