Effect of Citrus Root Exudates on Germination of Chlamydospores of the Vesicular-Arbuscular Mycorrhizal Fungus, Glomus epigaeum

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Abstract
The effect of root exudates from Troyer citrange (Poncirus trifoliata .times. Citrus sinensis) on germination of surface-sterilized chlamydospores of the vesicular-arbuscular mycorrhizal (VAM) fungus, G. epiagaeus, was examined on water agar. Optimum temperature for spore germination was 25.degree. C. After 7 day exposure of spores to root exudates, germination was increased from < 10% (distilled water control) to up to 27%. Germ tube length of exudate-treated spores was > 4 times greater than that of untreated spores. Root exudates stimulated branching of germ tubes; germ tubes of untreated spores branched infrequently. Root exudates apparently affect spore germination and germ tube growth of G. epigaeus and thereby could influence subsequent root colonization and VAM formation.