Resistance mechanisms of Septoria tritici to antifungal products of Pseudomonas

Abstract Growth of isolate ISR398A1 of the wheat pathogen Septoria tritici was suppressed for four days by 40 ppm of 1-hyroxyphenazine (phOH), an antibiotic excreted by Pseudomonas aeruginosa strain LEC1. Growth was resumed in the fifth day, when no more phOH could be detected in the culture medium. Addition of a protease preparation from the growth medium of Pseudomonas LEC1 did not effect the growth of S. tritici in culture. The presence of phOH in the culture induced an increase in the cellular activity of one of the three catalase isozymes found in conidia of S. tritici and of the one superoxide dismutase synthesized by the fungus, while the cellular activity of the peroxidase was lowered by this treatment. Addition of the antibiotic resulted in a 42% increase in melanin production by the fungus, which was not affected by the addition of protease. The addition of the antibiotic and the protease together, increased melanin production by 117%. The synergism between the phenazine derivative and the protease in the induction of oxidative stress is discussed in terms of the potential for proteolysis of the fungal proteins.