SCREENING FOR POTENTIAL ANTAGONISTS OF PSEUDOCERCOSPORELLA-HERPOTRICHOIDES, THE CAUSAL AGENT OF EYESPOT DISEASE OF CEREALS .1. BACTERIA

Bacteria isolated from wheat seedlings, plants or straw from several field sites were screened for antagonism towards the cereal eyespot pathogen Pseudocercosporella herpotrichoides on several media of differing nutrient status. Thirteen out of 348 isolates inhibited pathogen growth on low-nutrient media and several also prevented spore germination or reduced germ tube extension. These were selected for further tests on wheat seedlings inoculated with the eyespot fungus. Twelve known bacterial antagonists of other fungal plant pathogens were tested in vitro using the same methods, and the majority showed some activity towards P. herpotrichoides. Selected isolates were equally inhibitory to both W and R pathotypes of the fungus. Effects of potential antagonists on disease development were assessed by scoring lesions or by counting the number of infection plaques formed by the fungus on leaf sheaths. Two isolates of Pseudomonas fluorescens, along with a commercial strain of Streptomyces griseoviridis, showed activity both in vitro and in subsequent infection trials with plants and may therefore be of potential value as antagonists of P. herpotrichoides.