Differentiation of Xanthomonas campestris pv. pruni from Other Yellow-Pigmented Bacteria by the Refractive Quality of Bacterial Colonies on an Agar Medium. R. D. Gitaitis, Associate Professor, Department of Plant Pathology, Coastal Plain Experiment Station, Rural Development Center, University of Georgia, Tifton 31793-0748. J. D. Hamm, and P. F. Bertrand. Research Technician II, Department of Plant Pathology, Coastal Plain Experiment Station, and Associate Professor, Cooperative Extension Service, Department of Plant Pathology, Rural Development Center, University of Georgia, Tifton 31793-0748. Plant Dis. 72:416-417. Accepted for publication 14 December 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0416.

Epiphytic populations of Xanthomonas campestris pv. pruni were detected on peach leaves by spreading 0.1-ml aliquants from serial dilutions of leaf washes onto the surface of nutrient agar plates. After incubation at 30 C for 48–72 hr, petri plates were positioned 15 cm above a clear plastic template with horizontal black lines spaced 3 mm apart. The lined template was subilluminated by a fluorescent lamp light box. When the template was viewed through the bacterial colonies, various patterns were associated with different colony types. The clarity and refractive quality of colonies of X. c. pv. pruni created an undistorted image of discrete straight lines. Other yellow colonies distorted patterns or were opaque.