Sensitivity of fungi from cereal roots to fluquinconazole and their suppressiveness towards take‐all on plants with or without fluquinconazole seed treatment in a controlled environment

Abstract

The take‐all fungus, Gaeumannomyces graminis var. tritici, was highly sensitive to fluquinconazole (in‐vitro EC50 0·016–0·018 mg L−1), a fungicide developed for use as a seed treatment to control take‐all, and to prochloraz (EC50 0·006 mg L−1). Fungi of other genera that were commonly isolated from cereal roots were sensitive in varying degrees to prochloraz but were relatively insensitive (e.g. Fusarium culmorum, EC50 > 20 mg L−1) or slightly sensitive (e.g. Epicoccum purpurascens, EC50 0·514 mg L−1) to fluquinconazole. Gaeumannomyces graminis var. graminis and G. cylindrosporus, weak parasites that can protect roots against take‐all, and an unnamed Phialophora sp., all closely related to the take‐all fungus, were highly or moderately sensitive to fluquinconazole. Alternaria infectoria and E. purpurascens were most consistently effective in suppressing development of take‐all on pot‐grown wheat plants dual‐inoculated with G. graminis var. tritici and the nonpathogen. Take‐all was decreased more on dual‐inoculated wheat plants grown from seed treated with fluquinconazole or fluquinconazole plus prochloraz than when only an antagonistic fungus (A. infectoria, E. purpurascens, Fusarium culmorum or Idriella bolleyi) or a seed treatment was applied. These fungi were less effective in combination with seed treatments on barley. Gaeumannomyces graminis var. graminis and G. cylindrosporus, tested on wheat, suppressed take‐all only in the absence of fungicides. It is suggested that the performance of seed treatment containing fluquinconazole against take‐all may in some circumstances be enhanced by its partial specificity for the take‐all fungus.