Résumé
A bacterial strain, Streptomyces sp. CIMAP- A1 was isolated from Geranium rhizosphere and identified by morphological, physiological, biochemical and molecular characters (16S rDNA gene sequence). Phylogenetically, it was found most closely related to S. vinacendrappus, strain NRRL-2363 with 99% sequence similarity. The strain had potential antagonistic activity (in vitro) against wide range of phytopathogenic fungi like Stemphylium sp., Botrytis cinerea, Sclerotinia sclerotiorum, Colletotrichum spp., Curvularia spp., Corynespora cassicola and Thielavia basicola. The extracellular secondary metabolites produced by the strain in the culture filtrates significantly inhibited the spore germination, growth of germ tube of the germinated spores and radial growth of Alternaria alternata, Colletotrichum acutatum, Curvularia andropogonis and Fusarium moniliforme. The extraction of culture filtrate with solvents and purification by following VLC and PTLC methods always yielded a 10th fraction antifungal compound showing activity against wide range of phytopathogenic fungi. The strain was able to produce siderophores and indole-3-acetic acid. The strain was found to enhance the growth and biomass production of Geranium. It increased 11.3% fresh shoot biomass of Geranium and 21.7% essential oil yield.