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Strains of Pseudomonas solanacearum from Central and South America: A Comparative Study. E. R. French, Plant Pathologist, North Carolina State University Mission, AID, Lima, Peru; L. Sequeira, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 60:506-512. Accepted for publication 20 October 1969. DOI: 10.1094/Phyto-60-506.

Forty-two isolates of Pseudomonas solanacearum from solanaceous and musaceous hosts in both North and South America, including 11 isolates from the Amazon River basin, were compared with respect to colony morphology, melanin formation, and pathogenicity under greenhouse conditions. Size, shape, coloration and slime deposition in colonies of isolates grown on a tetrazolium medium, and melanin formation in a tyrosine medium, were useful in the classification of isolates into races and strains. Differential hosts were Musa balbisiana, susceptible to race 2 isolates only, and eggplant (Solanum melongena), susceptible to all race 1 isolates. Peruvian race 2 isolates from the Amazon River basin were similar to race 2 isolates from Colombia in pathogenicity, colony characteristics, and host range. Both groups of isolates reportedly are insect-transmitted, causing Moko disease on plantains (Musa Groups AAB and ABB). The present Moko disease epiphytotic in Peru is advancing upstream along the Amazon River at about 22 km/year, and it is suggested that the disease has spread from Colombia into Peru. All Peruvian Amazon basin race 2 isolates had identical pathogenic potential on various hosts, and could be distinguished from the Central American insect-transmitted strain (SFR) on the basis of colony morphology. Because the Amazon isolates appeared to belong to a distinct, stable group, they have been designated as race 2, strain A. An Amazon isolate of race 1 was not pathogenic to tobacco, a characteristic shared by only a few isolates from the North American continent.