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

Bark beetle-associated fungi in Fennoscandia with special emphasis on species of Ophiostoma and Grosmannia

“…The best-known examples of the latter group are the Dutch elm disease pathogens, Ophiostoma ulmi (Buisman) Nannf. and Ophiostoma novo-ulmi Brasier, species responsible for the disastrous pandemics killing millions of elm (Ulmus L.) trees in both Europe and North America during the past century (Gibbs 1978, Brasier 1991, Hubbes 1999, Brasier and Kirk 2001. Other severe pathogens include the host-specific varieties of Leptographium wageneri (W.B.…”

“…Most studies have focused on the Scolytus Geofroy spp. vectoring the Dutch elm disease fungi (Gibbs 1978, Brasier 1991, Hubbes 1999, Brasier and Kirk 2001. In this unusual fungus-vector system, the hardwood-infesting bark beetles have rather fixed associations with non-native fungi.…”

Ecological impacts of non-indigenous invasive fungi as forest pathogens

“…and other species of elm (Bey 1990). White elm has been planted extensively in rural as well as urban settings (Hubbes 1999). The prolific seed production by healthy elm trees gives the species an important ecological role because the seed is consumed by many species of birds and small mammals.…”

Wood production, wood technology, and biotechnological impacts

“…Next to fighting the fungus directly, attempts to control the disease target on reduction of insect vector populations (Hubbes 1999). Fungi infectious to the beetle´s larvae exist (Houle et al 1987) but have so far not given rise to a biological control programme.…”