BIOLOGICAL-CONTROL OF SOILBORNE PLANT-PATHOGENS BY A BETA-1,3 GLUCANASE-PRODUCING PSEUDOMONAS-CEPACIA

A beta-1,3 glucanase-producing bacterium identified as Pseudomonas cepacia was isolated on a synthetic medium with laminarin as sole carbon source. In biocontrol experiments carried out under greenhouse conditions, this bacterium decreased the incidence of diseases caused by Rhizoctonia solani, Sclerotium rolfsii and Pythium ultimum by 85, 48 and 71%, respectively. A determination of lytic enzymes revealed no chitinolytic activity. However, an active and stable beta-1,3 glucanase was detected. The optimal temperature and pH values for its activity were 60-degrees-C and 5.0, respectively. The induction of this beta-1,3 glucanase by different fungal cell walls as sole carbon source in synthetic medium was correlated with the biocontrol of the respective fungi by Pseudomonas cepacia. The damage caused to R. solani hyphae was observed under light and electron microscopes. The role of the beta-1,3 glucanase produced by Pseudomonas cepacia in the biological control of soilborne plant pathogens is discussed.