Field control of take‐all of wheat by avirulent fungi

SUMMARY In field experiments in New South Wales, wheat inoculated with Gaeumannomyces graminis var. tritici had less take‐all and yielded significantly more grain ( P ≤ 0·05) when simultaneously inoculated with G. graminis var. graminis and a lobed hypho‐podiate Phialophora sp. synonymous with Phialophora radicicola Cain var. radicicola sensu Deacon than when unprotected with these fungi. An isolate of P. radicicola var. graminicola did not confer any protection. The yields of cross‐protected wheat approached those of healthy wheat where take‐all incidence was slight to moderate while control was less economically significant where disease was severe. If this form of control proved similarly effective against natural inoculum it might be best employed at the beginning of a wheat monoculture after a break crop and serve to delay the onset of severe take‐all. A preliminary survey of 28 wheat fields in New South Wales using a bait technique and examining for characteristic fungal structures showed that G. g. graminis was rarely present in the soil and the lobed hyphopodiate Phialophora sp. and P. r. graminicola were absent. Significant populations of G. g. graminis only occurred in first wheat crops after a long period of native pasture. In New South Wales, at least, these avirulent fungi would have to be introduced to wheat fields for take‐all control.