Control of Rhizoctonia solani in a tobacco-float system using low rates of iprodione- and iprodione-resistant strains of Gliocladium roseum

Results obtained using low rates of the fungicide iprodione- and iprodione-resistant strains of Gliocladium roseum to control Rhizoctonia solani Kühn (Teleomorph: Thanatephorus cucumeris (Frank) Donk) in a tobacco float system are reported. The objectives were three-fold: to obtain G. roseum (GNL) strains resistant to the fungicide iprodione; to verify that the mutants maintained the same characteristics of the wild type; and to control R. solani in a tobacco float system by the application of low doses of fungicide combined with a resistant biological control agent (BCA) strain. Two resistant strains were obtained and the IC50 values were 44.7 and 5000 μg ml−1 for GNL wild type and mutants, respectively. The results showed the same level of disease control in plots with a high rate of iprodione and in plots with a low rate of fungicide, applied together with GNLr1 (96%) and GNLr2 (98%) iprodione-resistant strains of G. roseum. Less-disease control was obtained by a reduced dose of iprodione, when applied alone.