Extracellular enzyme profiles of the fungal pathogen Rhizoctonia solani isolate 2B-12 and of two antagonists, Bacillus megaterium strain B153-2-2 and Trichoderma harzianum isolate Th008 .1. Possible correlations with inhibition of growth and biocontrol

Cell-free culture filtrates of the fungal plant pathogen Rhizoctonia solani isolate 2B-12, causal agent of soybean (Glycine max) root rot, inhibited the growth of the biocontrol agents Bacillus megaterium strain B153-2-2 and Trichoderma harzianum isolate Th008. The pathogen secretes endoproteinase, exochitinase, glucanase, and phospholipase all of which are potentially detrimental to the cell wall/membrane integrity of the biocontrol agents. Compared to R. solani 2B-12, the soilborne fungus T. harzianum isolate Th008 produced more extracellular endochitinase and endoproteinase, both of which could be disruptive of the cell wall and membrane structure of R. solani 2B-12. In contrast to both R. solani 2B-12 and T. harzianum Th008, the rhizosphere competent bacterium B. megaterium B153-2-2 produced a relatively large amount of extracellular endoproteinase and phospholipase. The calcium-dependent neutral endoproteinase secreted by B. megaterium B153-2-2 is capable of inactivating, to varying degrees, four of the extracellular enzymes produced by R. solani 2B-12. We also report on the activity of several extracellular enzymes which has not been previously reported for either R. solani or T. harzianum. (C) 1996 Academic Press Limited.