Assessing management strategies for mitigating Rhizoctonia damping-off in sugar beet cultivation

Rhizoctonia solani is recognized as one of the most economically significant pathogens that can cause both crown root rot (CRR) and damping-off (DO) in the sugar beet (SB) plant. This report details the first investigative study on R. solani as a fungus causing DO of SB in Morocco. The identification of the fungal pathogen was done both based on morphological features as well as on molecular tools utilizing internal transcribed spacer region of ribosomal DNA (ITS rDNA) and specific primers. In vitro evaluation of the antifungal effect of four commonly used fungicides, tebuconazole, azoxystrobin, trifloxystrobin, and difenoconazole, revealed their effectiveness in inhibiting the growth of pathogenic strains on potato dextrose agar (PDA) medium. Bacillus subtilis Y1336, available in the market, was tested as a potential biocontrol agent (BCA) against R. solani -induced DO. The effectiveness of the BCA was confirmed through double culture tests on PDA, in vitro seed inoculation with both B. subtilis and R. solani , and by employing the antagonist agent as a seed coat in greenhouse settings. This marks the first instance of the effectiveness of B. subtilis Y1336 against R. solani- induced DO in SB. B. subtilis Y1336 should be integrated into SB damping-off control strategies, in conjunction with the fungicides that have been shown to be more effective. • Rhizoctonia solani is a key pathogen responsible for sugar beet damping-off in Morocco. • Treatment with difenoconazole or tebuconazole individually effectively inhibited the mycelial growth of R. solani strains. • Bacillus subtilis Y1336, a commercial bacterium, showed a mycelial growth inhibition rate of R. solani exceeding 74 %. • In vitro bioassay, Sugar beet seed coating with B. subtilis Y1336 reduced Rhizoctonia damping off by 75.43 %. • Under greenhouse conditions, seed treatment with B. subtilis Y1336 reduced Rhizoctonia seedling damping off by 58.75 %.