Abstract

A. Anitha and M. Rabeeth

In vitro tests of interactions between Streptomyces griseus strains and some soil-borne plant pathogens (Fusarium oxysporum, Alternaria alternate, Rhizoctonia solani and Fusarium solani) and 2 isolates of Aspergillus flavus were studied on PDA medium. Strains tested produced a metabolite that inhibited growth of plant pathogenic fungi on PDA medium (dual culture test). When grown in liquid medium having fungal cell walls as sole carbon source, S. griseus produced chitinase enzyme in the medium. Higher levels of this enzyme were induced by cell wall of Aspergillus flavus and the crude chitinase enzyme extracted showed zone of inhibition on all pathogens inoculated PDA plates at all tested concentrations. When lytic enzyme produced by S. griseus was incubated with hyphal wall of the test fungi treated with 2 M NaOH and chloropharm: Methanol, the release of glucose and N acetyl glucosamine significantly increased relative to the untreated one. This result suggests that proteins in the cell walls of pathogens may make these walls more resistant to degradation by the extracellular lytic enzymes. Ionic strength of NaOH on lytic activity was tested, where as the enzymes lysed fungal cell wall best at ionic concentration of 2 M treatment. Pretreatment with alkali or proteolytic enzyme increases their susceptibility for lysis. In vitro lytic activity provides an appropriate condition and the effect of biocontrol organism in field level treatment.