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Bacterial Blight of Cassava in Colombia: Epidemiology and Control. J. C. Lozano, Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706; L. Sequeira, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 64:83-88. Accepted for publication 19 July 1973. DOI: 10.1094/Phyto-64-83.

Dispersal by splashing raindrops is the most important means of dissemination of the cassava blight bacterium (a possible strain of Xanthomonas manihotis) within localized areas in Colombia. Dissemination from one area to another occurs through propagation of infected plant parts and by means of infested tools. In controlled inoculation experiments in the field, plant-to-plant spread occurred in the direction of prevailing winds, and disease incidence was correlated with amount of rainfall. However, no dissemination occurred when host plants were located at least 15 m away from the inoculum source. Satisfactory disease control was obtained by excising upper portions of infected plants and allowing the stumps (20-30 cm) to resprout. Effectiveness of this control method was reduced when treating highly susceptible, severely infected cultivars. Rooting excised buds was an efficient method of obtaining healthy planting stock from infected cultivars. Eight out of 1,293 cassava cultivars tested under greenhouse conditions were resistant to bacterial blight. Resistance was dependent on restriction of penetration and systemic invasion by the pathogen; two cultivars (‘M. Col. 647’ and ‘M. Col. 667’) exhibited a hypersensitive response which limited the size of leaf lesions. The use of resistant cultivars remains the most promising method of control of the disease in the tropics.