ABSTRACT
Brasier, C.M. and J.N. Gibbs. MBC tolerance in aggressive and non-aggressive isolates of Ceratocystis ulmi. Ann. Appl. Biol. 80:231-235.
In view of the interest in the fungicide benomyl and its breakdown product, methyl benzimidazole-2-ylcarbamate (MBC), for the control of Dutch elm disease (Ceratocystis ulmi) in Britain and North America, and of increasing reports of tolerance to benzimidazoles in other fungi the following study was made to assess the potential for emergence of tolerant strains in C. ulmi. In selection experiments, tolerance to 0.5 ppm MBC occurred at a frequency of approximately 1 in 1.3 X 108 conidia in both aggressive and nonaggressive isolates of Ceratocystis ulmi. The tolerant strains were inhibited by 5 ppm MBC, however, and attempts to select strains tolerant to 10 ppm were unsuccessful. In each of three isolates examined, tolerance remained stable after 15 successive transfers on fungicide-free medium. Genetic control was nuclear and probably conditioned by a single gene. It is thought unlikely that the appearance of tolerant strains in nature will jeopardize the use of MBC for the control of Dutch elm disease.
Magasi, Laszlo P., 1975. Identification of Ceratocystis ulmi, based on production of coremia in vials. Bi-monthly Research Notes 31(2): 13. Canadian Forestry Service.
Culturing large numbers of samples suspected of containing Ceratocystis ulmi (Buisman) C. Moreau, the causal fungus of Dutch elm disease, is time-consuming. The surface sterilized twig sections are peeled, then small wood chips are aseptically removed and transferred to petri dishes containing potato dextrose agar. After some experimentation a new method was tested for reliability before being adopted as a routine laboratory technique for determining C. ulmi from samples suspected of Dutch elm disease. The advantages of the described technique include: 1) reduction in culturing time, resulting in up to ten-fold increase in the number of samples that can be handled by persons with minimum training in culture techniques; 2) reduction in media preparation, saving both time and culture medium; 3) reduction in the number of contaminated samples because no media other than the natural wood section is involved; 4) reduction in examination time, due to the reduction in the need for microscopic mount preparation; and 5) maintenance of the reliability of the chip-plating technique.
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