Ophiostoma
ulmi (Ceratocystis ulmi),
the causal agent of Dutch Elm Diseaes, was first isolated in 1920 in The Netherlands.
The disease was already widespread in this area, as well as Belgium and France,
at this time. It was first recorded in Britian in 1927, but very little damage
was observed, only 10-20% of the elm population was killed. During the late
1960's however a new agressive strain of the disease moved into England. This
new epidemic killed about 70% of the approximately 22 million elms in southern
England. This aggressive form entered The Netherlands in 1972 and France and
Germany in 1973.
Dutch Elm disease was not only found in Europe but North America as well. It spread from three main points, tri-state area surrounding New York City, central Indiana, and the Quebec Province of Canada. It was found in Ohio in 1930 but the most serious epidemic appeared in New York City in 1933.
So
what is Dutch Elm disease? It is a very destructive disease that effects all
elm species (the American elm is affected most severely). It first appears
as a sudden or prolonged wilting of the leaves of a single branch (or even
the entire tree).
Individual branches that are wilting are referred to as "flags"
(pictured left, courtesy Chad
Behrendt at the University of Minnesota) . The wilted
leaves turn chlorotic, curl and eventually drop from the tree. Most affected
branches will eventually die (Picture to the right from Dr.
Jim Deacon's web site The
Microbial World. For more info on this and others
diseases check out his web site.).
Dutch elm disease may be the result of a fungal pathogen, but this fungal pathogen owes much of its success to an insect. The Scolytus multistriatus (European elm bark beetle) and Hylurgopinus rufipes (Native elm bark beetle) are imporant factors in transmitted fungal spores from an infected tree to another tree. Also transmission of the disease can occur through root grafts. The fungus overwinters in the bark of dying or dead trees as mycelium or as spore bearing coremia (below left, picture courtesy of Chad Behrendt, University of Minnesota). The female beetle (preferring to lay eggs in the intersurface of the bark and wood of weakened trees) tunnels through the bark and opens a gallery in which she will lay the eggs. The eggs hatch and the larvae open tunnels at right angles. When they emerge and leave for another host they take with them spores they picked up from the coremia.
More Information about the Role of Women in the discovery of the cause of Dutch Elm disease coming soon.
