APPLICATION OF BIOCONTROL FUNGI IN GRANULAR FORMULATIONS OF PREGELATINIZED STARCH-FLOUR TO CONTROL DAMPING-OFF DISEASES CAUSED BY RHIZOCTONIA-SOLANI

Pregelatinized starch-flour granules containing fermentor-produced bio mass of the biocontrol fungi Gliocladium virens, isolates Gl-3 and Gl- 21, and Trichoderma hamatum, isolate TRI-4, protected eggplant, pepper , and zinnia seedlings from damping-off caused by the pathogen Rhizoct onia solani in a soilless mix. The granules contained more than 10(6) colony-forming units/g of product of the biocontrol fungi which repres ented a 64, 91, and 43% survival of the formulated biomass of Gl-3, Gl -21, and TRI-4, respectively. The survival of R. solani in pathogen-in fested beet seed and its ability to grow saprophytically from the beet seed into two soils were significantly reduced in both soils but depe nded upon the choice of antagonist and the amount of granules used. Th e saprophytic growth of R. solani was always reduced to a greater exte nt than was survival of R. solani in the beet seed. Isolates Gl-3 and Gl-21 were more effective in reducing pathogen populations at lower gr anular concentrations than was isolate TRI-4. The incidence of Rhizoct onia damping-off of eggplant in soilless mix was reduced (> 50%) with as little as 0.2% (w/w) of Gl-3 and Gl-21 granules and 1.0% (w/w) of T RI-4 granules, but plant stands were not as high as that in noninfeste d soilless mix (99%), Preparations with as little as 2.5% biomass of G l-21 added to soilless mix at a rate of 1.0% (w/w) were as effective a s a rate of 0.20% (w/w) granules containing 20% biomass in reducing da mping-off of eggplant. Similar results were observed with damping-off of pepper. These data suggest the importance of spatial distribution o f the biocontrol product in disease control. Formulations of Gl-3 and Gl-21 at rates of 0.2, 0.4, and 0.8% (w/w) prepared with 20% biomass w ere equally effective in reducing damping-off of zinnia in soilless mi x. Although high rates of TRI-4 granules also effectively reduced dise ase, none of the biocontrol formulations yielded a zinnia stand compar able to that in noninfested soilless mix (97%). (C) 1995 Academic Pres s, Inc.