Altered growth of Fusarium oxysporum f. sp. chrysanthemi in an in vitro dual culture system with the vesicular arbuscular mycorrhizal fungus Glomus intraradices growing on Daucus carota transformed roots

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Vesicular arbuscular mycorrhizal fungi can reduce plant disease symptoms and populations of pathogens through mechanisms that are not well understood. Glomus intraradices was grown on Daucus carota transformed roots in a two-compartment in vitro system. One compartment contained mycorrhizal roots on a complete growth medium, while the other contained a medium lacking sugar on which only mycelial growth was allowed. The direct interaction between G. intraradices and Fusarium oxysporum f. sp. chrysanthemi was studied in the compartment lacking sugar during a 5-day period. G. intraradices hyphal density and spore number were estimated along with F. o. chrysanthemi conidial germination, mycelial growth and sporulation. Five hours after inoculation, germination of F. o. chrysanthemi conidia doubled in the presence of G. intraradices. Radial growth of F. o. chrysanthemi colonies was always slightly but significantly enhanced in the presence of G. intraradices. No correlation was obtained between G. intraradices hyphae or spore densities and F. o. chrysanthemi hyphal growth. Overall sporulation of the 5-day-old F. o. chrysanthemi colonies was not influenced by the presence of G. intraradices. However, significant negative correlations were found between F. o. chrysanthemi conidia production and G. intraradices hyphae or spore concentrations. G. intraradices increased F. o. chrysanthemi conidial germination and slightly stimulated its hyphal growth in dual culture without any root influences. No antibiosis was observed between the fungi. The significance of the results and their potential implication for rhizosphere biology are discussed.