Identification of three Streptomyces strains and their antifungal activity against the rubber anthracnose fungus Colletotrichum siamense

Colletotrichum siamense causes rubber tree anthracnose and significant losses for the natural rubber industry. Here, actinomycete strains YQ-33, QZ-9 and WZ-2 were isolated, found to have high antagonistic activity against C. siamense and preliminarily identified as Streptomyces sp. Millet broth was the optimal medium for all strains to produce antifungal metabolites against C. siamense , and the millet broth culture filtrate from each strais greatly inhibited conidial germination and appressorial formation of C. siamense . Of the three strains, QZ-9 had relatively broad antifungal activity; its culture filtrate provided inhibition rates over 80% against mycelial growth of seven plant pathogenic fungi. Culture filtrates of QZ-9 and WZ-2 also reduced lesion size on rubber tree leaves and are promising candidates for control of rubber anthracnose.