Entomopathogenic fungi decrease<i>Rhizoctonia</i>disease in potato in field conditions

<i>Rhizoctonia</i> potato disease is widespread in the world and causes substantial yield and quality losses in potato. This study aimed to evaluate the efficacy of entomopathogenic fungi <i>Metarhizium robertsii</i> and <i>Beauveria bassiana</i> in the inhibition of potato <i>Rhizoctonia</i> complex disease. The efficacy of the entomopathogenic fungi <i>M. robertsii</i> and <i>B. bassiana</i> in the defense of potato against <i>Rhizoctonia</i> disease (stem cancer, black scrulf and other forms of manifestation on tubers) was estimated under field conditions in Western Siberia. Preplanting treatment of the tubers with <i>B. bassiana</i> decreased <i>Rhizoctonia</i> disease in the stems and stolons. At the same time, treatment with <i>M. robertsii</i> did not cause a decrease in <i>Rhizoctonia</i> disease in these organs. However, both fungi decreased the sclerotium index on the tubers of new crops. We demonstrated two mechanisms of inhibition of <i>Rhizoctonia solani</i> by <i>M. robertsii</i> and <i>B. bassiana</i>, including (1) direct effect, expressed as inhibition of <i>R. solani</i> sclerotium 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 with <i>B. basiana</i> can effectively manage <i>Rhizoctonia</i> disease during the plant vegetative season and that both fungi significantly improve the quality of the new tuber crop.