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Synergy between Achromobacter sp. and Pseudomonas phaseolicola Resulting in Increased Disease. A. L. Maino, Assistant Research Plant Pathologist, M. N. Schroth, Professor, and V. B. Vitanza, Staff Associate, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 64:277-283.

A bacterium frequently associated with Pseudomonas phaseolicola in culture was a mild pathogen of bean.  Physiological-morphological characteristics and a GC ratio of 41.8% indicated that this was an Achromobacter sp.  The number of lesions incited by P. phaseolicola increased from 2- to nearly 4-fold when inocula were mixed with Achromobacter sp.  Disease enhancement was observed regardless of whether inoculation was by infiltration, mechanical abrasion, or light spray, and whether Achromobacter was inoculated simultaneously or prior to inoculation with P. phaseolicola.  All Achromobacter strains tested and one strain of P. syringae enhanced infections of P. phaseolicola.  In contrast, P. marginalis and P. fluorescens decreased the number of lesions when mixed with P. phaseolicola.  P. phaseolicola multiplied logarithmically in bean leaves following a 12-15-hr lag phase.  The amount of growth, however, was greater when the Achromobacter sp. was added to the inoculum.  Although populations of the Achromobacter remained at a relatively low steady rate when singularly inoculated into primary leaves, the bacterium became systemic and was later isolated from noninoculated, symptomless plant parts.