Biocontrol of sclerotinia stem rot (Sclerotinia minor) in sunflower by seed treatment with Gliocladium virens

An isolate of Gliocladium virens from disease-affected soil in a commercial sunflower field proved highly antagonistic to Sclerotinia minor in culture. Significant disease control was obtained when a conidial suspension was applied over a limited area of potting medium and lateral roots were inoculated outside the treated area at the edge of the pot. Most promising, in terms of minimizing the amount of G. virens required for disease control, was the significant bioprotection obtained by seed treatment. In glasshouse experiments following inoculation of lateral roots with S. minor at 6-7 weeks after sowing, disease incidence was reduced from 60.0% to 15.8% in pelting medium and from 66.7%;, to 12.5% in field soil. Seed treatment was also effective in field microplots, where disease incidence was reduced from 37.0% to 22.2%. G. virens applied on seed did not affect the dry weight of the lateral root system.