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Biocontrol of Tobacco Brown-Spot Disease by Bacillus cereus subsp. mycoides in a Controlled Environment. Deborah R. Fravel, Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607; Harvey W. Spurr, Jr., Research Plant Pathologist, Southern Region, Agricultural Research Service, U.S. Department of Agriculture, Oxford Tobacco Research Laboratory, Oxford, NC 27565, also Professor of Plant Pathology, North Carolina State University, Raleigh. Phytopathology 67:930-932. Accepted for publication 7 February 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-930.

Sixteen bacterial isolates, primarily from tobacco leaf surfaces, were screened in vitro for effects on spore germination and germ tube development of three Alternaria alternata isolates. Most bacterial isolates suppressed number of germ tubes, and the length and branching of the longest germ tube. Appressorium formation data were inconclusive, but tended toward inhibition. Bacterial isolates which were most inhibitory to growth of A. alternata in vitro also were most inhibitory to that fungus on the leaf surface. Using this in vitro system, five bacterial isolates were selected for foliar biocontrol tests. A Pseudomonas maltophilia isolate did not alter lesion severity. Two bacterial isolates reduced lesion severity significantly. One isolate, Bacillus cereus subsp. mycoides, effectively controlled tobacco brown-spot lesion development in a controlled environment. Microscopic observations of the leaf surface showed that conidial germination was 10% in the presence of B. cereus subsp. mycoides, whereas, 98% germinated in the control and produced brown-spot symptoms.