INTERACTION BETWEEN ALTERNARIA-ALTERNATA OR FUSARIUM-EQUISETI AND GLOMUS-MOSSEAE AND ITS EFFECTS ON PLANT-GROWTH

The effect of inoculation with the saprophytic fungi Alternaria altern ata or Fusarium equiseti on maize (Zea mays) and lettuce (Lactuca sati va) with or without arbuscular mycorrhizal (AM) colonization by Glomus mosseae was studied in a greenhouse trial. Plant dry weights of non-A M-inoculated maize and lettuce were unaffected by the presence of A. a lternata and F. equiseti. In contrast, A. alternata and E. equiseti de creased plant dry weights and mycorrhization when inoculated to the rh izosphere before C. mosseae. The saprophytic fungi inoculated 2 weeks after G. mosseae did not affect the percentage of root length colonize d by the AM endophyte, but did affect its metabolic activity assessed as succinate dehydrogenase activity. Although F. equiseti inoculated a t the same time as G. mosseae did not affect mycorrhization of maize r oots, its effect on AM colonization of lettuce roots was similar to th at with A. alternata. In the rhizosphere of both plants, the populatio n of saprophytic fungi decreased significantly, but was not affected b y the presence of G. mosseae. Our results suggest that there may have been a direct effect of the saprophytic fungi on the mycorrhizal fungi in the extramatrical phase of the latter, and when the AM fungus was established in the root the AM fungus was less affected by the saproph ytic fungi.