CHARACTERIZATION AND BIOCONTROL POTENT OF STREPTOMYCES SP. ISOLATED FROM THE RHIZOSPHERE OF ONONIS ANGUSTISSIMA LAM.

Abstract

A total of 40 actinomycetes isolated from rhizosphere soils of Ononis angustissima Lam. were in vitro tested for their antagonism against deferent pathogenic microorganisms by streak assay. Among the isolates, four (21, 2A26, 1B10 and 2C34) present a potent antagonism against both pathogenic bacteria and fungi, they were selected, identified by 16S rDNA sequence analysis and phenotypic properties, and tested for their antimicrobial activity as well as their biocontrol potential against Chickpea (Cicer arietinum L.) pathogenic fungus (Fusarium oxysporum). Cultural characteristic studies strongly suggested that these strains belong to the genus Streptomyces. The four Streptomyces sp., solubilize phosphate and produce extracellular fungal cell-wall degrading enzymes chitinase and protease, as well as a marked production of acid-β-indole acetic (AIA). The nucleotide sequence of the 16S rRNA gene of Streptomyces sp. strains 21, 2A26, 1B10 and 2C34 exhibited close similarity (62-75%) with Streptomyces parvulus MARS 16S rRNA genes. The inhibition was higher against fungi and Gram+ bacteria, while Gram- bacteria were less inhibited. The growth of the plant pathogenic fungus Fusarium oxysporum was considerably inhibited in the presence of the strains 21, 2A26, 1B10 and 2C34 culture supernatant. These studies revealed that the presence of the Streptomyces strains in the soil significantly promoted the growth of the Chickpea plants. These results indicate that the Streptomyces strains isolated for rhizosphere from Ononis angustissima Lam. growing in arid conditions in southern Algeria (Sahara) could be an interesting source for antimicrobial bioactive substances and as biocontrol agents.