PHOSPHORUS CONCENTRATIONS IN PLANTS RESPONSIBLE FOR INHIBITION OF MYCORRHIZAL INFECTION

SUMMARY Using a ‘split root’ technique, it was found that phosphorus fertilization of half of the root system of sudangrass could significantly reduce the number of chlamydospores of the mycorrhizal fungus Glomus fasciculatus in the unfertilized half of the root system. In a second experiment, vials of soil containing different concentrations of phosphorus were inserted into pots of sudangrass which were fertilized with different amounts of phosphorus and inoculated with G. fasciculatus. The numbers of chlamydospores, vesicles and arbuscles and the amount of hyphae produced by G. fasciculatus on roots within the vials were not influenced by the soil P in the vials but were inversely correlated with the concentration of P in roots outside the vial. All evidence indicates that it is the concentration of P within the plant and not the soil P which leads to a reduction in colonization, infection, and spore production of G. fasciculatus.