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 sensi tive to fluquinconazole (in-vitro EC50 0.016-0.018 mg L-1), a fungicide dev eloped 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 relat ively insensitive (e.g. Fusarium culmorum, EC50 > 20 mg L-1) or slightly se nsitive (e.g. Epicoccum purpurascens, EC50 0.514 mg L-1) to fluquinconazole . Gaeumannomyces graminis var. graminis and G. cylindrosporus, weak parasit es that can protect roots against take-all, and an unnamed Phialophora sp., all closely related to the take-all fungus, were highly or moderately sens itive to fluquinconazole. Alternaria infectoria and E. purpurascens were mo st consistently effective in suppressing development of take-all on pot-gro wn wheat plants dual-inoculated with G. graminis var. tritici and the nonpa thogen. Take-all was decreased more on dual-inoculated wheat plants grown f rom seed treated with fluquinconazole or fluquinconazole plus prochloraz th an when only an antagonistic fungus (A. infectoria, E. purpurascens, Fusari um culmorum or Idriella bolleyi) or a seed treatment was applied. These fun gi were less effective in combination with seed treatments on barley. Gaeum annomyces graminis var. graminis and G. cylindrosporus, tested on wheat, su ppressed take-all only in the absence of fungicides. It is suggested that t he performance of seed treatment containing fluquinconazole against take-al l may in some circumstances be enhanced by its partial specificity for the take-all fungus.