Abstract

In this work, a wide survey and collection of agricultural soils from different habitats of the Al-Kharj region, Saudi Arabia, were conducted. 110 isolates of actinomycetes were isolated from these samples. Among them, 25 actinomycetes isolates were found to be antagonistic to Fusarium oxysporum, Macrophomina phaseolina and Sclerotium rolfsii. Only one isolate, denoted RDS16 had the strongest antagonistic activity against all of the tested fungi. This isolate was identified as Streptomyces tendae RDS16 based on morphological, cultural, physiological and molecular analyses. In addition, the optimal culture conditions for production of antifungal metabolites were investigated. The obtained results showed that incubation of S. tendae RDS16 for 4 days at 30°C and an initial pH of 7.5 on a fish-meal extract medium containing galactose as carbon source and casein as nitrogen source exhibited the highest production of antifungal compounds.

Key words: Antifungal activity, Fusarium oxysporum, Macrophomina phaseolina andSclerotium rolfsii.