COMPARATIVE INVESTIGATIONS ON THE ANTAGONISTIC ACTIVITY OF FLUORESCENT PSEUDOMONADS AGAINST GAEUMANNOMYCES-GRAMINIS VAR TRITICI IN-VITRO AND IN-VIVO

886 isolates, which were able to produce siderophores, were tested for their antagonistic activity against the test fungus Gaeumannomyces gr aminis var. tritici in vitro. 65% of the isolates proved to be effecti ve antagonists. By addition of Fe3+ to the nutrient medium, it could b e shown that besides siderophores other inhibitors are also involved i n the growth-inhibiting effect. 73 isolates were tested in pot trials in the greenhouse. The application of fluorescent pseudomonads was car ried out in form of a seed treatment of wheat. A total of 55% of the i n vitro active antagonists and 73% of the isolates, which had no effec t in vitro, were able to reduce the attack by Gaeumannomyces graminis var. tritici and to increase the fresh weight of wheat plants. Obvious ly, there is no relationship between the antagonistic activity of indi vidual isolates in vitro and their efficacy in vivo. With regard to th e search for promising candidates for biological control under practic al conditions a pre-selection on artificial media, therefore, does not seem to be useful.