BIOCONTROL OF COTTON DAMPING-OFF CAUSED BY RHIZOCTONIA-SOLANI IN THE FIELD WITH FORMULATIONS OF TRICHODERMA-SPP AND GLIOCLADIUM-VIRENS

Preparations of isolates of the biocontrol fungi Trichoderma spp. and Gliocladium virens were evaluated during four growing seasons for their efficacy in preventing damping-off of cotton caused by Rhizoctonia solani in field plots artificially infested with the pathogen. Pathogen saprophytic activity and populations of the biocontrol fungi were monitored periodically in the soils. The preparations included bran/germlings (actively growing hyphae on bran), a powder (Pyrax/biomass), and alginate pellets containing milled fermentor biomass of the fungi. Of the three preparations, bran/germlings consistently prevented disease, reduced pathogen saprophytic activity and stimulated proliferation of populations of the biocontrol fungi. In all four years, bran/germling preparations of an isolate of T. hamatum (TRI-4) and an isolate of G. virens (G1-21) significantly prevented disease, and in three of the years gave a plant stand comparable to that of the non-infested plots. Pyrax/biomass preparations of G1-21 prevented damping-off in two of the four years, but stands similar to those of the non-infested plots were never achieved. Pyrax/biomass preparations of most other isolates used were ineffective in preventing disease. Alginate pellets of the isolates studied did not prevent disease in the two years in which they were applied to soil. Generally, Pyrax/biomass and alginate pellet preparations did not reduce pathogen saprophytic activity or stimulate an increase in numbers of antagonistic fungi.