Infections of the American Chestnut Tree

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Cryphonectria parasitica, a filamentous, ascomycete fungus, is the causal agent of the chestnut blight5,14 which was introduced to North America from Japan circa 190412,14.The chestnut blight infects all members of the Castanea family14, and some members of the genus Quercus though C. parasitica infections are superficial14. A C. parasitica infection typically begins at a branch node or wound in the tree’s bark 14. Once a spore has entered the tree, hyphal growth begins14. When the fungi’s hyphae reach the cambium, the xylem and phloem are blocked, cutting off the transport of water and nutrients and a sunken canker is formed14. Eventually, the lack of water and nutrients kills the tree above the point of infection14. As a fungus, C. parasitica reproduces using both sexual spores (ascospores) and asexual spores (conidia) produced by stromata that erupt through the canker14. Ascospores are spread by the wind, while conidia are transported by water or animal vectors14. Most American chestnuts (Castanea dentata) survive for three to five years after being infected with the blight14. However, because C. parasitica only affects the tree above the root collar saplings, genetically identical to the original tree, grow back, perpetuating the cycle14. Before the introduction of C. parasitica, American chestnuts accounted for an estimated 25%-50% of all trees in the Appalachian Mountains13. Within 40 years of its introduction, the invasive parasite had killed nearly every American chestnut (Castanea denata) in the tree’s natural range13. In the centuries before the chestnut blight was introduced to North America, the American chestnut was a large, fast-growing canopy tree that dominated eastern forest13. The chestnut could reach a di... ... middle of paper ... ...-6074 10. Kwon B, Kim M, Park J, et. Al. Assessment of the core cryparin promoter from Cryphonectria parasitica for heterologous expression in filamentous fungi. Appl Mircobiol Biotechnol. 2009; 83:339-348 11. Liu Y, Double M, MacDonald W, Milgroom M. Persistence of Cryphonectria hypoviruses after their release for biological control of chestnut blight in West Virginia forsests. For. Path. 2002;32:345-356 12. Milgroom M, Cortesi P. Biological Control of Chestnut Blight with Hypovirulence: A Critical Analysis. Annu. Rev. Phytopathol. 2004;42:311-318 13. Oak, S. From the Bronx to Birmingham: Impact of Chestnut Blight and Management Practices on Forest Health Risks in the Southern Appalachian Mountains. Journal of the American Chestnut Foundation. 2002;16(1):32-41 14. Sinclair, Wayne, and Howard Lyon. Diseases of Trees and Shrubs. 2nd ed. Cornell University, 2005

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