Sensitivity of Phytomonas davidi to Antimicrobial Substances. Randolph E. McCoy, Professor, Agricultural Research and Education Center, University of Florida, Fort Lauderdale 33314. Plant Dis. 67:855-857. Accepted for publication 3 January 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-855.

Phytomonas davidi, a plant-infecting protozoan, was tested for sensitivity to 14 antimicrobial agents in liquid growth media. Cycloheximide, crystal violet, and a proprietary compound TC 1474 were inhibitory to growth at concentrations ≤1 μg/ml of medium. The antitrypanosomals, homidium bromide and berenil, were inhibitory at concentrations as low as 37 and 111 μg/ml, respectively, whereas quinine-HCl, trypanomycin, and sulfaquinoxaline had little or no effect at 1 mg/ml, the highest concentration tested. Three antibacterial and two antifungal compounds had little effect on growth of P. davidi, indicating their possible value in formulating selective media. P. davidi, collected from naturally infected Chamaesyce hypericifolia (spurge) and placed in dilutions of the growth-inhibiting compounds, reacted similarly except to cycloheximide, which showed little or no direct toxicity to either wild or cultured P. davidi. None of the tested compounds had activity against P. davidi in C. hypericifolia plants treated by root immersion.

Keyword(s): Trypanosomatidae.