sign in sign up
<<
Home , American chestnut, Beech, Castanea mollissima, Chestnut blight, Cryphonectria, Fagaceae

FORFS 20-03 University of Kentucky College of Agriculture, Food and Environment American , Cooperative Extension Service Castanea dentata Megan Buland and Ellen Crocker, Forest Health Extension, and Rick Bennett, Pathology

merican chestnut (Castanea den- tata) was once a dominant ,A historically found throughout eastern and comprising nearly 1 of every 4 in the central Ap- palachian region. Valued for its nuts (eat- en by people and a key source of wildlife ), rot resistance and attractive timber, it was a central component of many east- ern forests (Fig. 1). However, the invasive ( parasitica), introduced to North Amer- ica from in the early 1900s, wiped out the majority of mature throughout its range. While American chestnut is still functionally absent from these areas, continued ef- forts to return it to its native range, led by several different non-profit and academic research partners and using a variety of different approaches, are underway and provide hope for restoring this species. Figure 1. Large healthy American chest- Figure 4. Larger trunks and branches have nuts like this, once valued for timber, are deep vertical furrows. Species Characteristics now very rare. Most succumb to chestnut blight when they are much younger. American chestnut is a member of the Photos courtesies: Figure 1: USDA Forest Service - Southern Research Station, USDA Forest Service, family, the same family to SRS, Bugwood.org; Figure 4: Megan Buland, University of Kentucky which and trees belong. The and branches of American chest- oblong in shape, 5-8” long, with a coarsely serrated margin, each serration ending in are alternate in arrangement (Fig. a bristle tip (Fig. 3). Leaves are dark green above, pale below and are neither waxy nor 2). Leaves are simple and lanceolate or hairy. The are shiny and dark brown in color and resemble tiny footballs held closely against the branches. The bark of younger branches is a deep brown color and is covered in small, pale lenticels. The bark on larger branches and the trunks of larger trees is a dull grey color, with vertical fissures separating the bark into plates and ridges (Fig. 4). Male () and female flowers appear together on mature trees in the summer (Fig. 5). These develop into , 2-3 nuts held within

Figure 3. The margins of American chest- Figure 5. Spike-like male flowers (catkins) Figure 2. The leaves of American chestnut nut leaves are serrated, ending in a bristle are conspicuous during the summer when are alternate and serrated. tip. in bloom and have a distinctive smell. Photo courtesy: Ellen Crocker, University of Kentucky Photo courtesy: Ellen Crocker, University of Kentucky Photo courtesy: USDA Forest Service - Southern Re- search Station, USDA Forest Service, SRS, Bugwood.org

Cooperative Extension Service | Agriculture and Natural Resources | Family and Consumer1 Sciences | 4-H Youth Development | Community and Economic Development to the blight when young and trees may These are the -producing struc- grow, and thrive, in the forest understory tures of the , which produces or canopy gaps until reaching heights of these fruiting bodies instead of the more up to 15 meters and a trunk diameter commonly recognized mushroom-type of 20 centimeters.2 At this size, the tree structures produced by many other fungi. becomes more susceptible to infection However, these serve the same by the chestnut blight fungus. Trees purpose and airborne yellow spores from growing in the dense forest understory infected tissue can reach new hosts and are less likely to become infected by wind continue the cycle of infection. Other Figure 6. of the American chestnut, dispersed fungal spores and may remain signs of disease include wilted, yellowing spine covered burs. uninfected longer than trees growing in leaves (signs of water stress as the tree’s Photo courtesy: Paul Wray, Iowa State University, more open conditions. Only the above- vascular system is compromised), epi- Bugwood.org ground portion of the tree is impacted cormic shoots and root sprouts (Fig. 9). by chestnut blight. Following the death Figure 7. The nuts of American chestnut were a highly valued food source by hu- of a central trunk by the blight, root sys- mans and wildlife alike. tems may send up many shoots that can Photo courtesy: USDA Forest Service - Southern Re- thrive until they reach a sufficient size to search Station, USDA Forest Service, SRS, Bugwood. themselves be infected. For this reason, org it is not unusual to see small or bush-form American chestnut in forests. However, it is important to note that these trees are still susceptible to the blight and above ground shoots will continue to be killed Figure 9. Branch dieback symptoms by the fungus over time. caused by chestnut blight. The fungus infects susceptible trees Photo courtesy: Ignazio Graziosi, University of through wounds or cracks in the bark. Kentucky, Bugwood.org Once infected, trees exhibit sunken lesions, called cankers, on trunks and Chemicals produced by the pathogen branches as the fungus kills the tree’s directly inhibit the formation of callus tis- cambium. Cankers are characterized by sue which trees normally produce to wall 3 cracked, discolored bark (Fig. 8). Bright off and compartmentalize infections. orange tendrils or pustules may also Secretion of the metabolite by sometimes be observed in and around the fungus hampers the tree’s ability to these cankers, especially in wet weather. combat the infection, allowing the can- kers to continue to expand. Ultimately, a sharp, spike covered green bur that these cankers often cut off the movement turns to brown in the fall (Fig. 6 and 7). of water and nutrients between the roots and leaves of the chestnut tree, killing Chestnut Blight the vascular tissue of the tree around the Chestnut blight is caused by a non-na- canker. Small stems may be killed within tive fungal pathogen, Cryphonectria months of infection while cankers on parasitica, native to Asia, that infects larger trunks and branches may get pro- American chestnut trees and, in most gressively worse over several years. cases, ultimately leads to tree death. The While American chestnut is the spe- pathogen that causes chestnut blight was cies most impacted by chestnut blight in first found on American chestnut in 1904, North America, other chestnut species in ’s Zoological Park. In the are also impacted to varying degrees: decades following its initial detection it • American chestnut (C. dentata): most spread throughout the eastern US, killing susceptible, lethal infections 1 American chestnut as it progressed. 1 Rigling, D. and Prospero, S. (2018). Cryphonectria parasitica, American chestnut can still be found the causal agent of chestnut blight: invasion history, popula- in forests throughout the eastern United tion biology and disease control. Molecular , 19(1), 7–20. https://doi.org/10.1111/mpp.12542 States, though nearly always in the form 2 Paillet, F. (2002). Chestnut: History and Ecology of a Trans of immature trees growing from either Figure 8. Chestnut blight cankers, exhibit- formed Species. Journal of Biogeography. Vol. 29, No. 10/11. a seed or as sprouts from the roots of a ing orange sporulation and cracked, sunken https://www.jstor.org/stable/827566 bark. 3 Havir, E.A. and Anagnostakis, S.L. (1983). Oxalate produc- chestnut tree previously killed by blight. tion by virulent but not by hypovirulent strains of American chestnut is less susceptible Photo courtesy: Ellen Crocker, University of Kentucky parasitica. Physiol. Plant Pathol. 23, 369–376

2 • European chestnut (C. sativa): highly Other issues (Oxydendrum arboreum), and other plant susceptible, lethal infections In addition to Cryphonectria parasitica species that prefer similar site conditions. • Chinese chestnut (C. mollissima) and cinnamomi, American and Japanese chestnut (C. crenata): chestnut may also be affected by a number Research to bring back the low susceptibility, occasional minor of other native and non-native insects and American chestnut branch infections , particularly in the orchard or Hypovirulence: In addition, many species serve as hosts nursery setting, such as: Hypovirulence, the infection of a patho- to the pathogen, including like • Anthracnose and powdery mildew – gen by another infectious organism, has white oak (), scarlet oak (Q. native; foliar fungal pathogens given scientists some hope for reducing coccinea), and post oak (Q. stellata), and • Asian chestnut gall wasp, the severity of the chestnut blight due . These species are typically highly kuriphilus – non-native; insect pest to a loss of virulence of the pathogen. resistant to the pathogen and infection is making galls in and buds, Fungal viruses were discovered infecting noted to be most common for weakened larvae may lead to branch dieback and, the chestnut blight pathogen in , trees or when disease pressure is very in some cases of severe infestations, effectively weakening the blight and high. These hosts are likely to serve as a tree mortality reducing its ability to infect and kill long-term source of inoculum and, even • Japanese beetles – non-native; foliar European chestnut trees. Scientists here if American are absent from feeding beetles in the U.S. have experimented with hy- a site for a long time, the pathogen will • Periodical cicadas – native, insects lay povirulent strains of the chestnut blight persist in the environment ready to infect eggs in branches after feeding, wound- fungus that contains these viruses, in an American chestnut trees in the future. ing from oviposition (egg laying) may attempt to inhibit the ability of the fun- injure tree branches; neither larvae nor gus to kill American chestnuts, though Phytophthora root rot adults feed on the foliage or branches such research has yielded mixed results.5 Chestnut blight is not the only chal- • Ambrosia beetles – a mixture of native Some aspects of the relationship between lenge facing American chestnut trees in and non-native species. Beetles burrow the virus that causes hypovirulence in North America. Phytophthora root rot into trees, where they breed and rear chestnut blight, and the pathogen itself, (also called ink disease) is a root disease their young, it is the mutualistic fungi are not well understood and work in the caused by the non-native pathogen Phy- carried with them that may harm the 4Crandall, R. S., Gravatt, G.F., and Ryan, M.M. (1945). tophthora cinnamomi that has infested host tree Rot disease of Castanea species and some coniferous and American chestnut in its southern range • Weevils - a mixture of native species; broadleaf nursery stocks caused by . 4 since around 1824 . P. cinnamomi seems larvae burrow and feed inside the Phytopath. 35:162.:.180. to be most problematic for American chestnut fruits, destroying both its 5Milgroom, M.G. and Cortesi, P. (2004). Biological Control chestnut growing in lowland and clay culinary and economic value as well of Chestnut Blight with Hypovirulence: A Critical Analysis. Annual Review of Phytopathology. 42:1, 311-338. https:// throughout its range. as its viability to germinate and grow. www.annualreviews.org/doi/full/10.1146/annurev.phy- The causal agent of Phytophthora root to.42.040803.140325 rot is a borne oomycete. Oomycetes Distribution are “water-loving” and, while surveys have American chestnut has a historic range found P. cinnamomi present throughout that extends throughout the eastern the landscape in infected regions, it is , with the highest densities most commonly associated with disease located in the forests of the Appalachian in moist sites with poor soil drainage. Mountains (and its foothills). Today, It has proven especially challenging in American chestnut remains on the land- establishment of new orchards of Amer- scape and can still be found as stump ican chestnut as seedlings are particu- sprouts and understory trees. Dry, south larly susceptible. P. cinnamomi does not and east facing slopes with well-drained survive freezing temperatures well and, acidic soils are ideal site conditions for therefore, is most impactful to American American chestnut. While it can be chestnut in the southern parts of its range found growing in dense understory veg- where soil temperatures are milder in the etation, it is more common near roads winter. However, as the climate changes and forest edges, and other areas with the northern limit of P. cinnamomi may more sun exposure, which it can exploit push further north. P. cinnamomi has a to grow rapidly, outcompeting other broad host range extending far beyond under ideal conditions. Through- American chestnut and includes oak and out it is often found growing species in the eastern United States. Figure 10. Native range of the American alongside American beech (Fagus gran- chestnut tree (Castanea dentata). Little, E.L., However, in mature trees symptoms of P. difolia), chestnut oak (), Jr., 1977, Atlas of United States trees, volume cinnamomi infection can be difficult to mountain laurel (Kalmia latifolia), black 4, Minor Eastern : U.S. Depart- diagnose and its impact in forest settings cherry ( serotina), sourwood ment of Agriculture Miscellaneous Publica- overall is hard to assess. tion 1342, 17 p

3 lab has not easily been transferred to to chestnut blight, these trees do 6Kolp, M., Double, M., Fulbright, D., MacDonald, W. and Jarosz, M. (2020). Spatial and temporal dynamics of the field trials. Scientists have shown that appear to have higher resistance than fungal community of chestnut blight cankers on American it is transmissible as a therapeutic treat- pure American chestnuts.8 chestnut (Castanea dentata) in Michigan and Wisconsin. , Fungal Ecology, Vol 45, 100925. ment of individual cankers. But, success of hypovirulence at a forest population 7 Diskin, M., Steiner, K.C. and Hebard, F.V. (2006). Recovery Biotechnology: of American chestnut characteristics following hybridization level depends on the natural spread of the Another means of obtaining blight re- and backcross breeding to restore blight-ravaged Castanea virus. Studies suggest that environmental sistance in American chestnut through dentata. Forest Ecology and Management. Volume 223, Issues 1–3; Pages 439-447. https://www.acf.org/wp-content/ factors and vegetative incompatibility of breeding may lie in the use of biotech- uploads/2016/09/RecoveryofAmericanChestnutCharac- the chestnut blight fungus restricts virus nology to develop an American chestnut teristics-3.pdf 6 transmission. However, if researchers with the ability to tolerate the chestnut 8Westbrook, J.W., Zhang, Q., Mandal, M.K., Jenkins, E.V., can better understand the epidemiologi- blight. Scientists at SUNY’s College of En- Barth, L.E., Jenkins, J.W., Grimwood, J., Schmutz, J. and Hol- liday, J.A. (2019). Genomic selection analyses tradeoff cal dynamics of this system to determine vironmental Science and (ESF) between chestnut blight tolerance and inheritance crucial factors that limit establishment of are using a genetic modification approach from American chestnut (Castanea dentata) in (C. dentata x C. mollissima) x C. dentata backcross populations. BioRxiv hypovirulence in forest systems in North as a way to bring back the American 690693. doi: https://doi.org/10.1101/690693; https://www. America, hypovirulence may prove to be a Chestnut. The chestnut blight pathogen biorxiv.org/content/10.1101/690693v1.abstract valuable strategy for restoring American Cryphonectria parasitica, produces ox- 9Powell, W. and Newhouse. A. (2019) Developing Blight-Tol- chestnut long-term. alic acid (OA) among other chemicals erant American Chestnut Trees. Cold Spring Harbor, Perspectives in Biology. 12 (7). to produce cankers and eventually kill Hybridization: the cambium of the tree. But scientists Hybridization of susceptible American involved in The American Chestnut Re- chestnut with resistant species has long search and Restoration Project at ESF and been pursued as a possible means of collaborators at the American Chestnut developing a disease-resistant trees. Foundation, have identified a gene from Such attempts have been conducted by bread which potentially could crossing American chestnut with a re- enhance blight resistance by detoxifying sistant Asian chestnut species and then OA.9 This defense gene produces an en- backcrossing (crossing this hybrid tree zyme called oxalate oxidase (OxO) which back to another American chestnut) and blocks OA production by the fungus. By selecting for resistance to the blight. The transferring the OxO gene from wheat goal of this approach is that over time a (and a marker gene to help ensure the re- tree will be achieved that exhibits some sistance gene is present), into the chestnut level of the disease resistance of the Asian genome, the enzyme then protects the chestnut ancestor but the other growth tree, allowing the fungus and tree to co- traits of the American chestnut.7 To do exist. These blight tolerant trees can then this, typically American chestnut flow- be outcrossed to surviving mother trees ers are pollinated by Chinese chestnut and continued outcrossing may produce (). Chinese chestnut diverse and blight-tolerant trees over time. is mostly resistant to the effects of the pathogen; however, it has a smaller form and is not able to become a dominant forest tree. This hybridization approach has been spearheaded by The American Chestnut Foundation, in collaboration with a wide range of researchers, citizen scientists, and volunteers. Currently their program has seedlings that have been backcrossed for several generations, with a genetic make-up that is roughly 80-90% American chestnut and 10-20% Chinese chestnut in their composition. While results are mixed in terms of resistance

Educational programs of Kentucky Cooperative Extension serve all people regardless of economic or social status and will not discriminate on the basis of race, color, ethnic origin, national origin, creed, religion, political belief, sex, sexual orientation, gender identity, gender expression, pregnancy, marital status, genetic information, age, veteran status, or physical or mental disability. Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Nancy M. Cox, Director of Cooperative Extension Programs, University of Kentucky College of Agriculture, Food and Environment, Lexington, and Kentucky State University, Frankfort. Copyright © 2020 for materials developed by University of Kentucky Cooperative Extension. This publication may be reproduced in portions or its entirety for educational or non- profit purposes only. Permitted users shall give credit to the author(s) and include this copyright notice. Publications are also available on the World Wide Web at www.ca.uky.edu. Issued 10-2020

4