Interactions between Varieties of Gaeumannomyces graminis and Phialophora radicicola on Roots, Stem Bases and Rhizomes of tbe Gramineae

Abstract

SUMMARYInteractions between varieties of the take‐all fungus, Gaeumannomyces graminis (syn. Ophiobolus graminis) and of Phialophora radicicola on living hosts are considered. This follows the earlier recognition of both morphologically and ecologically different varieties of these fungi. Interactions occur between all combinations of these fungi tested, so the fungus common in British grasslands, P. radicicola var. graminicola, is not peculiar in being able to restrict colonization of roots by the take‐all fungus in unsterile soil. However, the outcome of these interactions (that is, both the direction in which and the intensity with which they occur) depends on (1) the relative inoculum levels of the fungi; (2) the host species or organ; it also depends on the relative inoculum potentials of the fungi. Thus, under suitable conditions the weakly and non‐pathogenic ones compete successfully with the pathogen, G. graminis var. tritici (wheat take‐all fungus) and so reduce disease levels. But this fungus, itself, can restrict growth of its potential competitors, which may explain why grass leys often carry‐over take‐all between cereal crops, because despite the known ability of P. radicicola var. graminicola on grass roots to compete with the pathogen, the pathogen population is at first much higher than that of P. radicicola var. graminicola.Possible explanations are offered as to why rhizomatous grasses commonly harbour the take‐all fungus in old pastures.Results of this and of previous work are discussed in relation to prospects for biological control of turf and cereal diseases caused by varieties of G. graminis and similar fungi, like Leptoshaeria narmari and L. korrae.