INTERACTION BETWEEN ASPERGILLUS-NIGER VAN TIEGH AND GLOMUS-MOSSEAE (NICOL AND GERD) GERD AND TRAPPE

Percent germination and length of hyphae of germinated Glomus mosseae spores, cultivated on water agar, decreased significantly in the prese nce of Aspergillus niger; this decrease was independent of any change in pH of the medium. Soluble and volatile compounds produced by A. nig er significantly decreased percentage spore germination and the hyphal length of G, mosseae on water agar. The decrease caused by volatile c ompounds was significantly greater when A, niger was grown on malt ext ract agar. Shoot dry weights of maize and lettuce plants cultivated in soil in pots, and percentage arbuscular mycorrhizal (AM) root coloniz ation of plants grown either in sand:vermiculite tubes inoculated with G. mosseae spores or in soil in pots with soil inoculum, were unaffec ted by A. niger when this saprobe was inoculated 2 wk after G. mosseae . Shoot dry weights and percentage AM colonization of plants decreased when the saprobic fungus was inoculated at the same time or 2 wk befo re G. mosseae. However, the metabolic activity resulting from AM colon ization, measured as the percentage of mycelium showing succinate dehy drogenase activity, decreased in all treatments. The population of A. niger decreased when inoculated to the rhizosphere of plants at the sa me time as, or 2 wk after, G, mosseae, but not when it was inoculated 2 wk before G, mosseae. Our results show that C. mosseae decreases the saprobic fungal population through its effect on the plant, whereas A . niger, by the production of soluble or volatile substances, inhibits G. mosseae in its extramatrical stage.