The soil borne fungus Rhizoctonia solani is one of the most destructive pathogens of sugar beet and many other plants belonging to more than 27 plant families. Root and crown rot of sugar beet caused by this pathogen is not efficiently controlled by resistance breeding and there is no cultivar completely resistant to this necrotrophic pathogen in any plant species. Therefore, an intensive use of other crop protection methods such as application of chemicals seems to be necessary to limit the damage in the fields. The growing concern about the negative environmental effects of fungicides and appearance of fungicide- resistant pathogen strains is motivating research for alternative protection strategies. Among such novel strategies, induced resistance has emerged as a potential supplement in crop protection measures. In the present study, we investigated the effect of riboflavin (vitamin B2) in activation of plant defense responses against R. solani. Riboflavin treated sugar beet plants showed lower disease index indicating capability of this vitamin in activating defense mechanisms and inducing resistance in the pathosystem. Molecular investigation of cprx1 gene expression, as a cationic peroxidase in sugar beet plants, revealed priming of this gene in riboflavin-treated plants inoculated with the pathogen compared to controls which were treated with sterile distilled water. Upregulation of cprx1 gene was correlated with enhanced lignin formation which is known as a structural barrier preventing pathogen invasion in plant cells.

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