Author(s): Sushmita Kalika-Singh, Luis Del Rio Mendoza and Mohamed Khan

Abstract: Cercospora leaf spot, caused by Cercospora beticola, is a major foliar disease of sugar beet (Beta vulgaris L.) that can substantially reduce yield and sugar quality. Effective management of CLS relies heavily on fungicides, particularly demethylation inhibitors (DMIs) and quinone outside inhibitors (QoIs). However, repeated and intensive use of these single-site fungicides has led to the emergence of resistant C. beticola populations, prompting increased reliance on multi-site protectants such as mancozeb. This study evaluated the sensitivity of 20 C. beticola isolates with varying resistance profiles to DMI and QoI fungicides, using mancozeb as a model multi-site fungicide. A randomized complete block design (RCBD) was implemented with two replicates per treatment, testing mancozeb concentrations ranging from 0.01 to 100 µg/mL. Mycelial growth was measured after 14 days, and the effective concentration required to inhibit 50% of fungal growth (EC₅₀) was calculated. Results indicated that isolates resistant to both DMI and QoI fungicides exhibited higher mean EC₅₀ values (15 µg/mL), suggesting reduced sensitivity to mancozeb, while isolates resistant to only one fungicide class or susceptible isolates showed lower EC₅₀ values (5 µg/mL). These findings highlight that dual resistance may contribute to emerging tolerance against multi-site fungicides. Although mancozeb remains broadly effective, the observed variability underscores the need for continuous monitoring of pathogen populations. Integrating fungicide rotation, tank-mixing strategies, and cultural practices within CLS management programs is essential to preserve the efficacy of available chemistries and mitigate resistance development.

DOI: 10.22271/27893065.2025.v5.i2b.151

Pages: 112-115 | Views: 119 | Downloads: 38

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