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).
USFS scientists and managers developed a conservation priority-setting framework for forest tree species at risk from pest & pathogens and other threats. The Project CAPTURE (Conservation Assessment and Prioritization of Forest Trees Under Risk of Extirpation) uses FIA data and expert opinion to group tree species under threat by non-native pests into vulnerability classes and specify appropriate management and conservation strategies. The scientists prioritized 419 tree species native to the North American continent. The analysis identified 15 taxonomic groups requiring the most immediate conservation intervention because of the tree species’ exposure to an extrinsic threat, their sensitivity to the threat, and their ability to adapt to it. Each of these 15 most vulnerable species, and several additional species, should be the focus of both a comprehensive gene conservation program and a genetic resistance screening and development effort. American chestnut and the closely related Appalachian and Ozark chinkapins are ranked among the five species most deserving of gene conservation and the development of resistance through breeding.
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.
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Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S., Prioritizing the conservation needs of US tree spp: Evaluating vulnerability to forest insect and disease threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/
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