Antimycotic Compounds from the Plant Pathogen Rhizoctonia solani and its Antagonist Trichoderma harzianum

The soilborne rhizosphere-competent fungal biocontrol agent Trichoderma harzianum isolate Th008 secreted trichodermin (MW = 292) and a small peptide (MW = 876) in culture. These compounds were antagonistic in culture to the mycelial growth of the soilborne fungal pathogen Rhizoctonia solani isolate 2B-12, which is highly virulent to soybean ( Glycine max )seedlings. When 100mg of dried autoclaved mycelial mat of R. solani was added to 200 ml liquid cultures of T. harzianum , the quantity of antimycotic compounds secreted by the latter was 3.5 times greater than that of the antagonist alone. R. solani secreted a coumarin derivative (MW = 313) in liquid culture, which inhibited the mycelial growth of T. harzianum ; however, inhibition of the growth of the antagonist required a greater concentration than that for the antimycotic compounds produced by the antagonist against the pathogen. The inclusion of 100 mg of dried autoclaved mycelial mat of T. harzianum in a 200 ml liquid culture of R. solani did not affect the quantity of the antimycotic compound produced by the pathogen.