Production of chitinolytic enzymes and endoglucanase in the soybean rhizosphere in the presence of Trichoderma harzianum and Rhizoctonia solani

Chitobiosidase, endochitinase, endo-beta 1-3-glucanase, and N-acetylglucosaminidase were detected in cell-free culture filtrates of the soilborne fungal biocontrol agent Trichoderma harzianum isolate Th008 and the roots of soybean seedlings (Glycine max cv. Williams 82). With the exception of endochitinase, activity of these enzymes also was associated with Rhizoctonia solani isolate 2B-12, causal agent of soybean root rot. In greenhouse experiments, soybean seeds inoculated with T. harzianum Th008 were planted in a soil mixture infested with R. solani 2B-12. At 15 days after emergence, the rhizosphere was assayed for chitinolytic enzymes and endoglucanase. Only N-acetylglucosaminidase and endochitinase activities in the rhizosphere samples mere significantly elevated above the controls. Using conventional specific enzyme assays and accepted methodologies including HPLC and native and SDS-PAGE slab-gels, it was determined that T. harzianum Th008 was the source of the endochitinase in the rhizosphere. On the other hand, the detectable levels of N-acetylglucosaminidase originated from the roots of soybean seedlings. (C) 1998 Academic Press.