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Characteristics of Colombian Isolates of Pseudomonas solanacearum from Tobacco. G. A. Granada, Research Assistant, Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin, Madison 53706; Luis Sequeira, Professor, Department of Plant Pathology, 1630 Linden Drive, University of Wisconsin, Madison 53706. Phytopathology 65:1004-1009. Accepted for publication 7 April 1975. DOI: 10.1094/Phyto-65-1004.

Bacterial wilt of tobacco, caused by Pseudomonas solanacearum, is widespread in the tobacco-growing areas of Colombia. All local cultivars are susceptible, and resistant cultivars from the United States are apparently susceptible under field conditions. The susceptibility of these cultivars could be attributed to strains of the pathogen that are different from those in other tropical and subtropical countries where the same cultivars have been grown successfully for many years. Under greenhouse conditions, however, five tobacco cultivars were resistant to P. solanacearum after stem inoculation with the most pathogenic of several isolates collected in Santander, Colombia. Resistance to these and other race 1 isolates could be overcome by increasing the number of stem inoculations per plant, or by inoculating plants at the seedling stage. Resistance to the Colombian or other race 1 isolates was not expressed in callus tissues derived from the resistant tobacco cultivar NC 95. Rates of colonization of callus tissues derived from both resistant and susceptible cultivars were very similar. Colombian isolates of P. solanacearum differed from a standard race 1 isolate from the United States (K60) only in relatively few physiological properties, among them: (i) their greater ability to utilize nitrate as the sole source of N, (ii) their lower tolerance to NaCl, and (iii) their ability to utilize malonate, tartrate, and L-phenylalanine as sole sources of C. In a wide variety of other physiological characteristics, such as utilization of many different carbohydrates and other organic compounds as sources of C, the production of lipase, catalase, oxidase, and tyrosinase, sensitivity to chemotherapeutants, etc., Colombian isolates were very similar to K60. It was concluded that breakdown of resistance under field conditions in Colombia is probably not due to the presence of unusual strains of the pathogen with high pathogenic potential.