Studies on vesicular-arbuscular mycorrhiza and fungal root pathogens of white clover and their interaction

Abstract

The role of a vesicular-arbuscular mycorrhizal fungus Glomus fasciculatus (Thaxter sensu Gerdemann) Gerdemann & Trappe in white clover (Trifolium repens L.) and its interaction with three fungal root pathogens Codinaea fertilis, Fusarium avenaceum (Fr.) Sacco. and Thielaviopsis basicola (Berk. & Br.) Ferraris was investigated. The growth responses of white clover to applied phosphorus and G. fasciculatus infection are shown in two P-deficient soils applied with a range of phosphorus levels. Growth was greatly stimulated by G. fasciculatus in both soils at all phosphorus levels, but the magnitude of the mycorrhizal response decreased with increasing phosphorus levels. Optical and transmission electron microscopes were first used to elucidate the mycorrhizal infection process and host response to infection. Some novel features including very thick-walled hyphae and intrahyphal hyphae within the host roots are recorded. C. fertilis, F. avenaceum and T. basicola were shown to be pathogenic on white clover, the infection and colonization of the roots being followed microscopically. The pathogens showed variable effects on plant yield under various experimental conditions of defoliation, plant age and inocula type. G. fasciculatus was shown to confer protection to white clover by reducing the detrimental effect of the pathogens under some conditions.