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Variability in Growth of Phytophthora cinnamomi Isolates in Response to Antibiotics. J. V. Leary, Associate professor, Department of Plant Pathology, University of California, Riverside 92521; G. A. Zentmyer(2), L. J. Klure(3), E. C. Pond(4), and G. L. Grantham(5). (2)(3)(4)(5)Professor emeritus, and staff research associates, respectively, Department of Plant Pathology, University of California, Riverside 92521. Phytopathology 72:750-754. Accepted for publication 15 October 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-750.

Growth rates of 35 isolates of Phytophthora cinnamomi (16 A1, 19 A2 mating type) from eight countries and 18 different hosts were compared at 25 C on media containing one of the following antibiotics: streptomycin, chlortetracycline, cycloheximide, nystatin, ethidium bromide, or chloramphenicol. Significant differences among isolates were observed in the presence of every single antibiotic, and several patterns of differential responses were apparent when the data were combined. The effect of streptomycin on P. cinnamomi was influenced by the nutrient medium used. On the average, the A1 isolates were significantly more resistant to cycloheximide than the A2 isolates. Most P. cinnamomi isolates were relatively sensitive to chlortetracycline and resistant to nystatin. Sensitivity of isolates to chloramphenicol correlated significantly with sensitivity to ethidium bromide and the response to chloramphenicol also correlated with the response to chlortetracycline. However, there was not a significant correlation between the effects of ethidium bromide and of chlortetracycline. Isolates with similar growth/temperature responses or isolates from the same host or geographic origin did not necessarily show the same pharmacological responses.

Additional keywords: adaptation, selective media, β -sitosterol, physiological races, polyene.