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1. INTRODUCTION
An as yet unidentified Arthrosporae fungus was encountered accidentally by Tsuneda and
Hiratsuka 1 at the Northern Forest Research Centre in Edmonton. The discovery,
reminiscent of the PeniciIlium case,l was made when a culture of a pathogenic fungus,
Ceratocystis ulmi, became contaminated with the unknown fungus. It soon became
apparent that the contaminant, when grown on potato dextrose agar (PDA), produces
substances which inhibit the growth of several tree disease causing fungi of the
Ceratocystis family.J,4
C, ulmi represents the perfect stage of an Ascomycetous fungus described as
Ceratostomel la ulmi by Buisman in 1923. This fungus also reproduces by means of an
imperfect stage, Pesotum ulmi,5 described by Schwarz in 1922. C. ulmi induces vascular
disease in elm trees. The disease has become known as the "Dutch elm disease", because it
was a Dutch botanist who f irst called attention to the disease in Holland in 1919. 6 The
infection was soon thereafter discovered in several parts of Europe and Asia.
The earliest known cases of the disease in North America were recorded in 1930
in Cleveland and Cincinnati. From 1930 to 1978 the disease spread over several parts of
the continent.
The occurrence of Dutch elm disease in Canada was first observed in 1944 in the
Province of Quebec. From 1944 to 1975, the disease gradually spread over other parts
of Canada. The most recent incidence of the disease was noted in Manitoba in 1975.
Newfoundland, Nova Scotia and the three most western provinces are still relatively free
of the disease.* Elm trees are found in most parts of the north temperate zone and are
planted in urban areas and in the countryside to provide shade, shelter and beauty.
The Dutch elm disease. called "the disease of the 20th century" is the most
devastating world-wide epidemic plant disease, Since its discovery in 1919, Dutch elm
disease has killed millions of elm trees in Europe and North America, causing billions of
dollars in direct economic losses and inflicting inestimable damage to the aesthetic quality
* The infections are already recorded in California and Manitoba. There is no
reason to believe that the Dutch elm disease will not spread to the three most
western provinces,