Abstract

One hundred and twenty-eight strains of actinomycetes were isolated from different soils in Riyadh region, Saudi Arabia. All isolates were screened for their antifungal activities against Rhizoctonia solani, Fusarium solani, Fusarium verticillioides, Alternaria alternata and Botrytis cinerea. A potent antagonist against all tested phytopathogenic fungi, designated RDS28, was selected and identified as Streptomyces spororaveusRDS28 according to analysis of 16S rRNA gene sequence. Factors affecting the production of the antifungal compounds were investigated. The results showed that incubation of S. spororaveus RDS28 for 72 h at 31°C and initial pH 7.5 on a medium containing glucose as a carbon source and proline as a nitrogen source gave the best antifungal antibiotic production. The culture filtrate of S. spororaveus RDS28 was extracted and purified and rechecked for their in vitro antifungal activities against the tested fungi. It can be concluded that, the antifungal antibiotic produced by S. spororaveus RDS28, demonstrated an obvious inhibitory effect on the tested pathogenic fungi.

Key words: Alternaria alternata, antibiotic, Botrytis cinerea, Fusarium solani, Fusarium verticillioides, Rhizoctonia solani.