ANTIMICROBIAL ACTIVITIES OF STREPTOMYCES PULCHER, S-CANESCENS AND S-CITREOFLUORESCENS AGAINST FUNGAL AND BACTERIAL PATHOGENS OF TOMATO IN-VITRO

Thirty-seven actinomycete species isolated from fertile cultivated soi ls in Egypt were screened for the production of antimicrobial compound s against a variety of test organisms. Most of the isolates exhibited antimicrobial activities against Gram-positive, Gram-negative, and aci d-fast bacteria, yeasts and filamentous fungi, with special attention to fungal and bacterial pathogens of tomato. On starch-nitrate agar, 1 4 strains were active against Fusarium oxysporum f.sp. hycopersici (th e cause of Fusarium wilt), 18 against Verticillium albo-atrum (the cau se of Verticillium wilt), and 18 against Altenaria solani (the cause o f early blight). In liquid media, 14 isolates antagonized Pseudomonas solanacearum (the cause of bacterial wilt) and 20 antagonized Clavibac ter michiganensis ssp. michiganensis (the cause of bacterial canker). The most active antagonists of the pathogenic microorganisms studied w ere found to be Streptomyces pulcher, S. canescens (syn. S. albidoflav us) and S. citreofluorescens (syn. S. anulatus). The antagonistic acti vities of S. pulcher and S. canescens against pathogenic fungi were as sessed on solid media, and those of S. pulcher and S. citreofluorescen s against pathogenic bacteria in liquid media under shaking conditions . The optimum culture conditions were determined.