MECHANISMS IN THE BIOCONTROL OF RHIZOCTONIA SOLANI-INDUCED COTTON SEEDLING DISEASE BY GLIOCLADIUM-VIRENS - ANTIBIOSIS

Production of the antifungal antibiotics gliotoxin and gliovirin by the biocontrol fungus Gliocladium virens has been associated with its efficacy as a biocontrol agent of seedling diseases incited by Rhizoctonia solani and Pythium ultimum. The association of gliotoxin and gliovirin with control of P. ultimum-incited disease has been confirmed by mutational analysis, but this is not true of gliotoxin and R. solani-incited disease. Gliotoxin-deficient (GLT-) mutants of G. virens were produced with UV and detected with Bacillus subtilis. Gliotoxin loss in the mutants was confirmed by high-pressure liquid chromatography analysis. Gliotoxin deficiency also results in loss of resistance to gliotoxin by GLT- strains. Assay of the GLT- mutants for suppression of R. solani-incited cotton seedling disease showed their biocontrol efficacy to be equal to that of the parent strains, indicating that gliotoxin is not necessary for protection of the infection court. These results and prior research put into question the importance of mycoparasitism and antibiosis as mechanisms in control of this disease, and suggest that the role of competition should be investigated more closely.