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Disease Control and Pest Management

Dosage Response of the Vesicular-Arbuscular Mycorrhizal Fungi Glomus fasciculatus and G. constrictus to Methyl Bromide. J. A. Menge, Assistant Professor, Department of Plant Pathology, University of California, Riverside, CA 92521; D. E. Munnecke(2), E. L. V. Johnson(3), and D. W. Carnes(4). (2)(3)(4)Professor, Research Assistant, and Postdoctoral Associate, respectively, Department of Plant Pathology, University of California, Riverside, CA 92521. Phytopathology 68:1368-1372. Accepted for publication 5 April 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1368.

Propagules of the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatus were fumigated with 3,000, 6,000, and 12,000 μliter methyl bromide (MB)/liter of air for periods varying from 1.5 to 48 hr. Propagules fumigated with MB at a CT (concentration time) less than 84,000 remained viable and were capable of infecting sudangrass. Glomus fasciculatus did not reproduce on the roots of sudangrass if inoculum was fumigated with 12,000 μliter air for 7, 12, and 15 hr (CT = 84,000, 144,000, and 180,000, respectively) or 6,000 μliter MB/liter air for 24 hr (CT = 144,000). Glomus fasciculatus remained viable when fumigated at 3,000 μliter MB/liter air for 48 hr (CT = 144,000). Dry weight of sudangrass was significantly (P = 0.05) reduced when seedlings were inoculated with G. fasciculatus inoculum which had been subjected to 12,000 μliter MB/liter air for 3 hr or longer (CT = 36,000) when compared to dry weight of sudangrass which received nonfumigated inoculum. Ninety percent of the chlamydospores of G. fasciculatus and G. constrictus failed to germinate when subjected to 12,000 μliter MB/liter air for 6 hr or more (CT = 72,000). No chlamydospores of either mycorrhizal fungus germinated when subjected to 12,000 μliter MB/liter air for longer than 8 hr (CT = 96,000). Glomus fasciculatus and G. constrictus are both more sensitive to MB fumigation than most soilborne plant pathogens. Furthermore, mycorrhizal fungi can readily be destroyed by MB fumigation in the top 45-cm of soil by most commercial MB fumigations.

Additional keywords: soil microbiology, plant nutrition.