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Identification of Low-Virulence Strains of Xanthomonas campestris pv. oryzae from Rice in the United States. R. K. Jones, Department of Plant Pathology and Microbiology, Texas A & M University System, College Station 77843, Present address: Department of Plant Pathology, University of Minnesota, St. Paul 55108; L. W. Barnes(2), C. F. Gonzalez(3), J. E. Leach(4), A. M. Alvarez(5), and A. A. Benedict(6). (2)(3)Department of Plant Pathology and Microbiology, Texas A & M University System, College Station 77843; (4)Department of Plant Pathology, Kansas State University, Manhattan 66506; (5)(6)Departments of Plant Pathology and Microbiology, University of Hawaii, Honolulu 96822. Phytopathology 79:984-990. Accepted for publication 5 May 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-984.

Rice plants exhibiting water-soaked lesions characteristic of a disease of bacterial etiology were observed on approximately 2,500 ha in Texas during the 1987 production season. Symptoms appeared following 20 days of nearly continuous rainfall that exceeded 50 cm at certain locations in the region. Lesions typically were associated with the leaf tips and edges, initially were water-soaked, and eventually appeared as bleached white to tan necrotic areas averaging 12 310 cm. Bacterial streaming was consistently associated with the vascular bundles of sectioned leaf specimens. Xanthomonas campestris pv. oryzae was recovered from plants exhibiting this symptom in 43 commercial fields in Texas and one field in Louisiana. Symptoms only were observed on recently introduced semidwarf cultivars derived from the suscept Taichung Native 1 (TN-1). Inoculation of 3-wk-old and 7-wk-old rice plants with bacteria isolated from lesions confirmed pathogenicity and reproduced symptoms observed in the field. Comparison of the causal organism with Asiatic strains of X. c. oryzae by standard biochemical tests, light and electron microscopy, fatty acid analysis, analysis of restriction fragment length polymorphisms, and reaction to monoclonal antibodies revealed numerous similarities but some consistent differences. Virulence of the U.S. strains on TN-1 was much reduced compared with strains from the Philippines. This is the first report of X. c. oryzae in the United States.

Additional keywords: bacterial leaf blight, Oryza sativa.