Mechanisms of inhibition of Gaeumannomyces graminis var. tritici by fluorescent pseudomonads

Abstract

The take‐all fungus Gaeumannomyces graminis var. tritici reduced the weight of wheat plants grown in tubes containing sterilized sand and plant nutrient solution. Fluorescent pseudomonads, when added to the tubes, inhibited the take‐all fungus and increased plant weight. Iron (as FeNaEDTA) had no effect on the inhibition of the fungus by the pseudomonads. Some of the pseudomonads produced a compound in the wheat rhizosphere with a UV absorption peak at 365 nm, but the inhibition of G. graminis by pseudomonads was not proportional to the UV absorbance of rhizosphere extracts. A yellow crystalline compound, absorbing at 365 nm, was extracted from broth cultures and shown to be toxic to G. graminis under acid conditions. This compound is considered to be phenazine‐I‐carboxylic acid.