Identification, pathogenicity, fungicide sensitivity and biological control of Rhizoctonia solani associated with damping-off disease of sugar beet in Morocco

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Abstract The fungus Rhizoctonia solani Kühn is an economically important pathogen involved in root rot and seedling damping-off disease of sugar beet (Beta vulgaris L.). In Morocco, this is the first detailed report of R. solani as the causative agent of sugar beet damping-off. The identification of the pathogen was based on combining the morphological characteristics and molecular characterization using the ribosomal DNA internal transcribed spacer (rDNA ITS) region. Antifungal activities of four commercial fungicides; azoxystrobin, difenoconazole, tebuconazole, and trifloxystrobin were assessed in vitro, displaying effective inhibition of the mycelial growth of the pathogen strains using PDA medium. A commercially available Bacillus subtilis Y1336 was evaluated as a potential biological control agent (BCA) against seedling damping-off caused by R. solani. The biological control activities of B. subtilis Y1336 was demonstrated by dual culture bioassays on PDA medium, in vitro seed inoculation with R. solani and B. subtilis, and by applying the BCA as seed coat under greenhouse conditions. This is the first time that the commercially available B. subtilis Y1336 has been proved as an effective BCA against the damping-off disease of sugar beet. This commercial antagonist should be incorporated into the integrated disease management startegy for sugar beet seedling mortality together with effective tested fungicides.

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