Partial separation of root exudate components and their effects upon the growth of germinated spores of AM fungi

Aseptic root exudates were collected from the liquid culture of roots of two host (Daucus carota and Lycopersicum esculentum) and one non-host plant (Beta vulgaris) of arbuscular mycorrhizal (AM) fungi. Exudate was also collected from maize (Zea mays FRB6) seedlings which were grown hydroponically under aseptic conditions. Exudate fractions of host roots stimulated hyphal branching behind any actively growing hyphal tip of three AM fungi tested (Gigaspora gigantea, G. rosea, and Glomus intraradices). Fractionation patterns obtained from C18 Sepak cartridges loaded with carrot root exudates isolated from roots grown under various phosphorus regimes, TLC analyses, and solubility properties of fractionated components, indicated a range of hydrophilic to hydrophobic hyphal branching stimulators. The 50/70% methanol fraction from a C18 cartridge induced hyphal branching patterns of G. gigantea that were dose dependent and were identical to those observed when germinated G, gigantea spores were grown with host roots in dual culture. Exudate fractions from B. vulgaris inhibited hyphal tip growth, but inhibited hyphal tips formed recovery branches which would allow continued fungal growth. These recovery hyphae were also formed when germinated G. gigantea spores were grown in dual culture with sugar beet roots. The recovery branches induced by non-host roots and the prolific branching induced by host roots have ecological implications.