Cryphonectria parasitica

Chestnut Blight - Cryphonectria parasitica (Murr.) Barr
 

Chestnut blight
Symptoms	Diseased tree

Chestnut blight
The American chestnut (Castanea dentata) and the related Allegheny and Ozark chinkapins (which are both varieties of Castanea pumila) were once important components of upland forests in eastern North America. American chestnut was the stalwart of eastern forests, where it is estimated it accounted for one-quarter of all the standing timber (USDA Forest Service, 1991), and provided Native Americans and European colonists with wood, tannin, food, and nuts for wildlife and domesticated animals. The much smaller chinkapins provided large crops of nuts that were preferred over chestnuts by wild turkeys (Minser et al., 1995).

Chestnut blight (=chestnut bark disease) was first reported in 1904, when cankers were observed in New York City (Merkel, 1905), although it was already widespread in the northeast at that time (Anagnostakis, 2001a). Chestnut blight is caused by an exotic fungus that attacks twigs, branches, and trunks, causing cankers that eventually girdle the tree. Metcalf & Collins (1909) believed that the disease was imported to North America in the late 1800s on Japanese chestnut (Castanea crenata) nursery stock, and distribution of successive importations was the major factor in the spread of the pathogen (Anagnostakis, 2001a). After its introduction, chestnut blight rapidly destroyed upland chestnut and chinkapin populations throughout eastern hardwood forests (National Academy of Sciences, 1975) over the next 60 years. By the 1950s, virtually all chestnut and chinkapins had been reduced to short-lived stump sprouts and disease-ridden shrubs (Burnham et al., 1986).

A considerable amount of research has been conducted on countering the effects of the chestnut blight pathogen. Introduction of strains of the fungus containing a virus that debilitates the blight fungus has been attempted (MacDonald & Fulbright, 1991; Anagnostakis, 2001b). Molecular manipulations of this virus (Choi & Nuss, 1992) have made transmission easier, and field experiments are in progress to evaluate effects and transmission. Breeding resistance into American chestnut from Asian species began at the Connecticut Experiment Station in 1930 and continues today (Anagnostakis, 2001a). Breeding for resistance has been conducted by other research programs and private foundations. The American Chestnut Foundation has completed a backcross breeding program involving transferring resistance from Chinese chestnut into American chestnut (sensu Burnham et al., 1986) and is planning on field testing progenies by 2006. The American Chestnut Cooperators Foundation is working within the American chestnut gene pool to develop resistance (Griffin, 2000). In breeding programs that utilize Asian germplasm, trees are being selected for both blight and P. cinnamomi resistance.

Sources
Anagnostakis, S. L. 2001a. The effect of multiple importations of pests and pathogens on a native tree. Biol. Invasions 3: 245-254.

Anagnostakis, S. L. 2001b. American chestnut sprout survival with biological control of the chestnut blight fungus population. For. Ecol. Managem. 152: 225-233.

Burnham, D. R., P. A. Rutter, and D. W. French. 1986. Breeding blight-resistant chestnuts. Plant Breed. Rev. 4: 347-397.

Choi, G. H. and D. L. Nuss. 1992. Hypovirulence of chestnut blight fungus conferred by an infectious viral cDNA. Science 257: 800-803.

Griffin, G. J. 2000. Blight control and restoration of the American chestnut. J. For. 98: 22-27.

MacDonald, W. L. and D. W. Fulbright. 1991. Biological control of chestnut blight: use and limitations of transmissible hypovirulence. Plant Dis. 75: 656-661.

Merkel, H. W. 1905. A deadly fungus on the American chestnut. New York Zool. Soc., 10th Ann. Rep., pp. 97-103.

Metcalf, H. and J. F. Collins. 1909. The present status of the chestnut bark disease. U. S. Dept. Ag. Bull. 141, part 5, pp. 45-53.

Minser, W. G., T. Allen, B. Ellsperman and S. E. Schlarbaum. 1995. Feeding response of wild turkeys to chestnuts in comparison with other mast species. Proc. 49th Ann. Meet. Southeast. Assoc. Fish Wildl. Agencies, p. 490-499.

National Academy of Sciences. 1975. Forest Pest Control. Washington, D. C.

United States Department of Agriculture Forest Service. 1991. Pest Risk Assessment of the Importation of Larch from Siberia and the Soviet Far East, Miscellaneous Publication No. 1495, September, 1991.