The American elm and Dutch elm disease

Abstract

Shortly after World War I, a new disease previously unknown among elms emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United States (1930), and Canada (1945), killing millions of elms. The disease known, as Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors. Numerous attempts to control the disease have concentrated on the reduction of insect vector populations, exploitation of natural host resistance, extensive application of fungicides and integrated pest management. In spite of these efforts in Canada, the disease continues to migrate westwards threatening the elm populations in Saskatchewan and Alberta. Today there are approximately 700 000 elm shade trees in cities and towns across Canada and their value exceeds $2.5 billion dollars.With the advance of molecular biology new, powerful tools are now available to study, in greater detail, the molecular and biochemical mechanisms of the DED pathogen, with particular reference to the mechanisms that induce host defenses. A glycoprotein has been isolated and identified such that when injected either in liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of both five-year old elm seedlings and 10 cm diameter trees. The elicitor induces a chain of defensive reactions that prevent the rapid spread of the fungus within the vascular system of the host. Key words: Ophiostoma ulmi, elm bark beetle vectors, induced resistance, chemical control, RFLP, mitochondrial DNA, ribosomal DNA, virus-like DNA, resistance breeding