Rhizoctoniapotato disease is widespread in the world and causes substantial yield and quality losses in potato. This study aimed to evaluate the efficacy of entomopathogenic fungiMetarhizium robertsiiandBeauveria bassianain the inhibition of potatoRhizoctoniacomplex disease. The efficacy of the entomopathogenic fungiM. robertsiiandB. bassianain the defense of potato againstRhizoctoniadisease (stem cancer, black scrulf and other forms of manifestation on tubers) was estimated under field conditions in Western Siberia. Preplanting treatment of the tubers withB. bassianadecreasedRhizoctoniadisease in the stems and stolons. At the same time, treatment withM. robertsiidid not cause a decrease inRhizoctoniadisease in these organs. However, both fungi decreased the sclerotium index on the tubers of new crops. We demonstrated two mechanisms of inhibition ofRhizoctonia solanibyM. robertsiiandB. bassiana, including (1) direct effect, expressed as inhibition ofR. solanisclerotium formation in cocultivation assays, and (2) indirect effect, which is associated with increased peroxidase activity in potato roots under the influence of colonization by entomopathogenic fungi. We suggest that the treatment of seed tubers withB. basianacan effectively manageRhizoctoniadisease during the plant vegetative season and that both fungi significantly improve the quality of the new tuber crop.

The immunosuppressive and insecticidal activity of culture of the entomopathogenic fungus Cordyceps militaris on the larvae of the Colorado potato beetle Leptinotarsa decemlineata has been established for the first time. It was found that the peroral effect of the fungal culture resulted in dose-dependent decrease in survival, delayed in development time and molting, decreases in the total hemocyt counts, increased activity of phenoloxidases in the hemolymph, and reduced activity of the enzyme in the cuticle, as well as increased sensitivity of larvae to the fungus Beauveria bassiana at the level of the synergistic effect.