Abstract
Biological control agents Trichoderma harzianum, Bacillus subtilis, and Streptomyces canescens.are known as effective biocontrol agents for several soil-borne fungal plant pathogens including Macrophomina phaseolina and Colletotricum fragariae. The present work was carried out in the suburbs of Tripoli, Libya, during the spring of 2009 to illustrate the antagonistic effect and mode of actions of these three bioagents against Macrophomina phaseolina and Colletotrichum fragariae isolated from strawberry plants.The antagonistic effects of the different bioagents against pathogens as well as the interactions between them were evaluated in-vitro in dual culture and illustrated by scanning electron microscope (SEM) technology . B. subtilis (B1), S. canescens and T.harzianum showed antagonistic effect when used against C. fragariae and gave 73.7, 72.5, and 65.0 % of inhibition, respectively. SEM showed that T. harzianum act through several mechanisms such as hyperparasitism causing destruction the mycelium of the pathogens. Also a malformation and lysis of hyphae were observed in the mycelium of M. phaseolina and C. fragariae due to different antibiotics and enzymes produced by B. subtilis and S. canescens.