Influence of glyphosate herbicide treatment of couch grass on take-all caused by <i>Gaeumannomyces graminis</i> var. <i>tritici</i> with the addition of soil-borne microorganisms
Couch grass rhizomes harbour Gaeumannomyces graminis var. tritici (Ggt), which causes take-all of wheat. Glyphosate used after cereal harvest to control couch can increase take- all in subsequent wheat crops. Following glyphosate treatment, the colonisation of senescing couch rhizomes by Ggt when treated with the endophytic fungus Microdochium bolleyi, and the spread of Ggt from senescing couch rhizomes to wheat when treated with the rhizobacterium Pseudomonas fluorescens, were investigated in two separate experiments. In Experiment 1, glyphosate increased Ggt inoculum in couch, irrespective of whether M. bolleyi was added to the potting medium. In Experiment 2, take-all severity and Ggt DNA concentration in roots of the accompanying wheat plants tended to decrease with glyphosate treatment of couch and increase only when P. fluorescens was added. Soil-borne microflora in fields containing glyphosate-sprayed couch may affect expression of take-all in subsequent wheat.