Detection of Pseudomonas Colonies That Accumulate Poly-?-Hydroxybutyrate on Nile Blue Medium. LUELLEN PIERCE, Department of Environmental Science, Policy and Management, University of California, Berkeley 94720. MILTON N. SCHROTH, Department of Environmental Science, Policy and Management, University of California, Berkeley 94720. Plant Dis. 78:683-685. Accepted for publication 28 March 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0683.

A simple procedure was developed to detect colonies of bacteria that accumulate poly- β-hydroxybutyrate(PHB), a storage product characteristic of many nonfluorescent pseudomonads. Colonies of PHB-positive bacteria fluoresced bright orange to yellow under long-wave ultraviolet light when grown on a medium containing PHB and Nile blue dye. Bright orange fluorescent granules were visible within the cells when examined microscopically under ultraviolet light. Colonies of fluorescent pseudomonads did not fluoresce on this medium, nor were fluorescent granules visible microscopically. This technique allows detection of PHB-positive pseudomonads without microscopic examination. Nile blue medium also was useful as a differential isolation medium for Pseudomonas solanacearum and may be useful for other nonfluorescent pseudomonads