Virulence of Xanthomonas campestris pv. translucens on Selected Wheat Cultivars. E. A. MILUS, Assistant Professor, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. D. B. CHALKLEY, Research Specialist, Department of Plant Pathology, University of Arkansas, Fayetteville 72701. Plant Dis. 78:612-615. Accepted for publication 21 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0612.

In this study, strains of Xanthomonas campestris pv. translucens from North and South America were examined for differences in virulence on a set of potential differential wheat cultivars. Seedlings of 19 wheat cultivars were inoculated with 81 strains of the pathogen isolated from wheat, barley, rye, or triticale and rated for percent water-soaking in the inoculated area 8 days after inoculation. Averaged over all cultivars, 69 virulent strains caused 14.4-38.1% water-soaking, and 12 weakly virulent strains caused 1.1-4.5%. Averaged over the 69 virulent strains, five susceptible cultivars had 43.4-75.0% water-soaking, and 17 resistant cultivars had 5.5-22.8%. The cultivar ? strain interaction was highly nonsignificant (P ? 0.9999) when data for the 69 virulent strains on the 19 cultivars were analyzed. Thus, there was no evidence for races among the strains that best represent strains capable of causing bacterial streak on wheat in the field. Cultivars rated as resistant to bacterial streak in the field are likely to remain resistant relative to susceptible cultivars, although actual disease severities may vary due to differences in inoculum level or environmental conditions.