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

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.