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 biomass 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 Rhizoctonia solani in a soilless mix. The granules contained more than 106 colony-forming units/g of product of the biocontrol fungi which represented 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-infested beet seed and its ability to grow saprophytically from the beet seed into two soils were significantly reduced in both soils but depended upon the choice of antagonist and the amount of granules used. The saprophytic growth of R. solani was always reduced to a greater extent 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 granular concentrations than was isolate TRI-4. The incidence of Rhizoctonia 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 TRI-4 granules, but plant stands were not as high as that in noninfested soilless mix (92%), Preparations with as little as 2.5% biomass of Gl-21 added to soilless mix at a rate of 1.0% (w/w) were as effective as a rate of 0.20% (w/w) granules containing 20% biomass in reducing damping-off of eggplant. Similar results were observed with damping-off of pepper. These data suggest the importance of spatial distribution of 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 were equally effective in reducing damping-off of zinnia in soilless mix. Although high rates of TRI-4 granules also effectively reduced disease, none of the biocontrol formulations yielded a zinnia stand comparable to that in noninfested soilless mix (97%).