American Chestnut Restoration 

Host: Joanna Coles, Warren County Extension Agent for Agriculture & Natural Resources
Guest: Dr. Ellen Crocker, Forest Health Extension Specialist
Topic: American Chestnut Restoration
Research to bring back the American Chestnut Hypovirulence: Hypovirulence, the infection of a pathogen by another infectious organism, has given scientists some hope for reducing the severity of the chestnut blight due to a loss of virulence of the pathogen. Fungal viruses were discovered infecting the chestnut blight pathogen in Europe, effectively weakening the blight and reducing its ability to infect and kill European chestnut trees. Scientists here in the U.S. have experimented with hypovirulent strains of the chestnut blight fungus that contains these viruses, in an attempt to inhibit the ability of the fungus to kill American chestnuts, though such research has yielded mixed results.5 Some aspects of the relationship between the virus that causes hypovirulence in chestnut blight, and the pathogen itself, are not well understood and work in the lab has not easily been transferred to field trials. Scientists have shown that it is transmissible as a therapeutic treatment of individual cankers. But, success of hypovirulence at a forest population level depends on the natural spread of the virus. Studies suggest that environmental factors and vegetative incompatibility of the chestnut blight fungus restricts virus transmission.6 However, if researchers can better understand the epidemiological dynamics of this system to determine crucial factors that limit establishment of hypovirulence in forest systems in North America, hypovirulence may prove to be a valuable strategy for restoring American chestnut long-term. Biotechnology: Another means of obtaining blight resistance in American chestnut through breeding may lie in the use of biotechnology to develop an American chestnut with the ability to tolerate the chestnut blight. Scientists at SUNY’s College of Environmental Science and Forestry (ESF) are using a genetic modification approach as a way to bring back the American Chestnut. The chestnut blight pathogen Cryphonectria parasitica, produces oxalic acid (OA) among other chemicals to produce cankers and eventually kill the cambium of the tree. But scientists involved in The American Chestnut Research and Restoration Project at ESF and collaborators at the American Chestnut Foundation, have identified a gene from bread wheat which potentially could enhance blight resistance by detoxifying OA.9 This defense gene produces an enzyme called oxalate oxidase (OxO) which blocks OA production by the fungus. By transferring the OxO gene from wheat (and a marker gene to help ensure the resistance gene is present), into the chestnut genome, the enzyme then protects the tree, allowing the fungus and tree to coexist. These blight tolerant trees can then be outcrossed to surviving mother trees and continued outcrossing may produce diverse and blight-tolerant trees over time.