SURVEY OF ANTIBIOTIC-RESISTANCE AND DEPENDENCE IN PHYTOPHTHORA

When culture blocks were incubated on V-8 agar plates containing 300 ppm streptomycin sulfate, mutants appeared as fast-growing sectors within 30 days. Streptomycin-resistant mutants were isolated from the sectors of both A1 and A2 mating types of P. parasitica, P. palmivora, P. capsici and P. cinnamomi. Streptomycin also caused mating type change in P. parasitica. Streptomycin-dependent mutants were also isolated from the fast-growing sectors of A2 isolates of P. parasitica and A1 and A2 isolates of P. palmivora, P. capsici and P. cinnamomi. Presence of CaCl2 in the medium induced a greater need for streptomycin for the dependent isolates of P. parasitica. Fast-growing sectors also appeared when culture blocks were incubated on medium containing 100 ppm chloramphenicol. Chloramphenicol-resistant mutants were isolated from sectors of A1 and A2 mating type of P. parasitica, P. palmivora, P. capsici and P. cinnamomi. By incubating streptomycin-resistant mutants of P. parasitica on medium containing chloramphenicol and vice versa, mutants resistant to both antibiotics were obtained.