Assessment of Crypilollectria pamsitica Hypovirulence in Chestnut Blight-Infected American Chestnut Trees (Castanea dentatal in Two Michigan Regions
Korb, Jennifer E.
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Chestnut blight, which has destroyed the American chestnut tree (Castanea dentata) population in the United States in the twentieth century, is caused by the fungal pathogen Cryphonectria parasitica. The discovery of hypovirulent C. parasitica strains, or those with a reduced capacity to cause the disease, sparked the hope for a possible biological control of the pathogen. In this study, virulence of blight-infected chestnuts was assessed in two Michigan regions: the northwest (Rau stand) and the southwest (Kellogg Biological Station). Using the Kellogg Forest trees as a comparative group, tests were conducted to assess C. parasitica pathogenicity in each canker. Those strains that showed reduced virulence were then tested for the presence of hypovirulent factors such as mycovirus infection (dsRNA) or mitochondrial abnormalities (cyanide-resistant respiration). In the Rau stand, where there are no healing cankers to suggest the presence of hypovirulence, a suspected hypovirulent strain was isolated from tree 8, stem B (strain 8B(2)). Although no hypovirulent factor was found in this strain, tests showed that the hypovirulence it possesses is capable of spreading to virulent strains. Further investigation of BB(2) will be conducted to determine the cause of hypovirulence and the possibility of its use as a biological control of chestnut blight in the Rau stand.