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Effect of Secondary Spread of Clavibacter michiganensis subsp. michiganensis on Yield of Northern Processing Tomatoes. Mark D. Ricker, Former Research Associate, Campbell Institute for Research and Technology, Campbell Soup Company, Napoleon, OH 43545. Richard M. Riedel, Professor, Department of Plant Pathology, The Ohio State University, Columbus 43210. Plant Dis. 77:364-366. Accepted for publication 5 November 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0364.

Test plots of the determinate tomato (Lycopersicon esculentum Mill.) cultivar Easy Winner were established in a field near Fremont, OH, in 19861988 to study the effects of dispersal of the bacterial canker pathogen on yield. Leaf symptoms indicative of secondary spread of Clavibacter michiganensis subsp. michiganensis were widespread in 1986 and 1987; in 1988, a single area (about 6 m in diameter) of symptomatic plants with marginal scorching of leaflets and fruit spotting was present. The bacterium systemically infected scattered plants throughout the field, not just in the scorched area, but caused little or no wilting. Yields of inoculated plants were greatly reduced, but compensation by adjacent plants allowed plots with inoculated plants to yield as much fruit as the control plots. A simple graphing procedure designed to relate average plant yield to distance from the closest inoculated plant was tested. Plants adjacent to inoculated ones yielded on average over the 3 yr 12% more than the mean of all noninoculated plants.