The role of antibiotic production by a strain of Pseudomonas fluorescens in the suppression of Pseudocercosporella herpotrichoides , the causal agent of eyespot disease of cereals

Abstract

Pseudomonas fluorescens strain 220 is an effective antagonist of Pseudocercosporella herpotrichoides, the eyespot pathogen of cereals. Culture filtrates of Ps. fluorescens 220 were inhibitory to spore germination and hyphal growth of P. herpotrichoides and at least two compounds with antifungal and antibacterial activity were identified in cultures grown in nutrient broth. In plant tests, both a culture broth of Ps. fluorescens 220 and a crude antibiotic extract reduced eyespot disease, whereas a mutant strain of 220 deficient in antibiotic production had no effect. Production of antibiotics would therefore appear to be a major factor in the suppression of P. herpotrichoides infection. A loss of disease control when Ps. fluorescens 220 was applied to plants in water was not due to lack of survival, as populations of a marked strain of Ps. fluorescens 220 applied to the stem base of wheat plants were similar whether applied in water or culture broth.