Dutch elm disease

Dutch elm disease

Scientific Article:

Dutch elm disease has often been referenced as one of the most destructive plant diseases known to man. The disease itself is caused by the ascomycete Ophiostoma ulmi (ascomycete is a grouping of fungus of the phylum Ascomycota that are characterized by bearing sexual spores in a specialized sac) in association with a secondary vector the scolytid beetles. Together with a this particular type of elm bark beetle, the disease has infected thousands of elm trees the world over and has had serious implications for forest ecosystems far and wide.

The particular historical and geographical origins of this phenomenon are difficult to trace with any degree of certainty but it is known that the disease appeared at several locations in northwest Europe around 1918-1921. Following its initial observation, it quickly spread across Europe and overseas to North America, through the Balkans, Turkey, and Ukraine and appeared in Central Asia some twenty years later. This rapid spread was the sign of the first epidemics breaking out in the 1920s and 1930s. Research however varies greatly as to where the origins of the disease itself originated. There is evidence to support the disease’s initial origins as Himalayan, European, or Chinese. The most popular of these hypotheses is that the disease began in China and later spread into Europe. This 'China hypothesis' has been based primarily on two lines of evidence. the first being the high level of resistance to the disease that the Chinese elm species have shown when compared to species of elm in Europe and North America. This resistance suggests that the fungus (Ophiostoma ulmi) may have evolved alongside the tree, explaining the more balanced relationship that has been observed. The second of the two lines of evidence that has been used to support the China hypothesis is the high species diversity of the Chinese elm. This point suggests that China could have been the evolutionary hub and consequently the hub of some of its diseases that it is associated with.

Ophiostoma ulmi is estimated to have made it to the United States by the early 1920s. It was brought in by unknowing furniture makers who imported European elm logs for use in making veneer grade products such as cabinets and tables. It has been predicted that some of the beetle vectors of the Dutch elm disease pathogens, the scolytid beetles, had been brought into the United States from Europe, years before the fungi itself was ever introduced.

Dutch scientist Marie Beatrice Schwarz was credited with having been the first to have identified the agent that causes the disease. The disease would later come to be called Dutch Elms Disease.

Prior to any outbreaks of the disease within the United States, elm trees were commonly used as street trees and were planted widely along walkways and roads in affective monocultures. Monoculture is cited as the main reason why Dutch Elm Disease had such devastating results on the towns and cities of the United States, with an estimated 40 million American elm trees have been killed as a result of the introduction of the disease.

The Dutch Elm Disease epidemics can be used as an example to help illustrate the value of diversity in plant populations, as well as the myriad of dangers inherent in globalization and the transportation of plant materials around the world.

Efforts to eradicate the disease in the United States have been generally unsuccessful. Some common steps that can be taken to prevent rapid spread include the aforementioned avoidance of planting monocultures of elm trees, the rapid removal of any and all dead or dying tree segments that are affected, and the breakage of root grafts between elms that are growing adjacently. For these measures to make a difference, diligent monitoring and inspection are required. Chemical management options for managing the disease have also been explored but are not widely used, as the insecticides used in efforts to kill the beetle vectors of the disease are expensive and not particularly effective (in addition to the negative ecological implications of heavy chemical use). As for a long term solution to the disease, breeding programs aimed at developing disease-resistant elms have been put in place. These programs vary in their practices, with some using Asian elm species that have high resistance to Dutch elm disease and attempting to introduce these traits to native elms. Other programs have targeted native elms directly by using the select few specimens that have shown natural resistance to the disease and cloning these individuals. 

By: Sabrina Smits 

 (Sherald)

Bibliography

Brasier, C. M. (1990). China and the origins of Dutch elm disease: an appraisal. Plant Pathology , 39, 5-16.

D’Arcy, C. J. (2000). Dutch elm disease. Retrieved University of Illinois, from American Phytopathological Society: http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/DutchElm.aspx

Sherald, J. Dutch elm disease symptoms. http://plantdiagnostics.umd.edu/level3.cfm?causeID=1208.