Aerial Dispersal of Xanthomonas campestris pv. campestris from Naturally Infected Brassica campestris. T. -L. Kuan, Research Manager, Plant Pathology, Asgrow Seed Company, San Juan Bautista, CA 95045. G. V. Minsavage, Research Assistant, Asgrow Seed Company, San Juan Bautista, CA 95045, and N. W. Schaad, Professor, Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow 83843. Plant Dis. 70:409-413. Accepted for publication 12 November 1985. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-409.

The importance of cruciferous weeds as a reservoir of inoculum and the role of aerial dispersal of Xanthomonas campestris pv. campestris (X. c. pv. campestris), causal agent of black rot of crucifers, was investigated. Leaves of Brassica campestris and air samples were collected in a naturally infected patch of B. campestris weeds in a noncultivated area. Leaves were sampled for X. c. pv. campestris by assaying tissue removed with a cork borer and by assaying wet filter-paper disks placed on leaf surfaces. We detected X. c. pv. campestris on surfaces of lesion areas and nonlesion areas of leaves. As many as 6.7 × 10⁷ cells per gram fresh weight were found on lesion areas of leaves. Leaf surface populations of X. c. pv. campestris on symptomless leaves decreased after periods of heavy rainfall and low nighttime temperatures of 0.6–6 C. Air samples were taken with an Andersen viable particle sampler during rain and periods of no rain. Counts of viable X. c. pv. campestris per cubic meter of air ranged from a high of 13.68 during rain to a low of 0.84 during dry periods. Aerosol dispersal of X. c. pv. campestris from cruciferous weeds could be an important primary source of inoculum.