GERMINATION AND HYPHAL GROWTH OF GLOMUS MOSSEAE IN VITRO: EFFECTS OF RHIZOSPHERE BACTERIA AND CELL-FREE CULTURE MEDIA

Summary-Germination and growth of chlamydospores of the vesicular-arbuscular (VA) mycorrhizal fungus G!omus n~osseae on water-agar medium under axenic conditions were compared after treatment with washed cells. cell-free supernatants and complete bacterial cultures. Spore germination was not affected by bacterial treatments. but the additions of complete bacterial cultures and cell-free supernatants significantly (P Q 0.05) stimulated hyphal growth and the number of new vegetative vesicles formed per germinated resting spore. INTRODL’CTION Cell-free culture media of rhizosphere bacteria were able to improve the formation of vesicular-arbuscular mycorrhizas (VAM) between Glomus mosw~r and several host plants (Azcon er al., 1978). This effect. which may bc accounted for by the ability of soil microorganisms to excrete biologically active substances (Lynch, 1976; Strzelczyk and Pokojska-Burdzicj, 1984). can be exerted indirectly through the host plant or directly on the fungus. Recent studies indicate that soil microorganisms can improve indc-pcndcnt hyphal growth from G. mosseae spores at the pm-infection stages (Azcon-Aguilar and Barea, 1985). Furthermore, isolated free-living micro-organisms were able to stimulate the axenic growth of G. mossecre on water agar (Azcon-Aguilar et al., 1986: Mayo t’t d.. 1986). This effect was achieved even without contact between microorganisms. A logical next step is to test the effect of cell-free supernatants from free-living microorganisms on the axenic development of G. mossear. The aim of this paper was to ascertain whether a soil bacterium which enhanced mycorrhizal formation and function in previous studies, is able to stimulate spore germi-nation and hyphal growth in citro. \lATERtALS AND METHOD