Fungicide resistance in Cercospora species causing cercospora leaf blight and purple seed stain of soybean in Argentina

Abstract

Cercospora species cause cercospora leaf blight (CLB) and purple seed stain (PSS) on soybean. Because there are few resistant soybean varieties available, CLB/PSS management relies heavily upon fungicide applications. Sensitivity of 62 Argentinian Cercospora isolates to demethylation inhibitor (DMI), methyl benzimidazole carbamate (MBC), quinone outside inhibitor (QoI), succinate dehydrogenase inhibitor (SDHI) fungicides, and mancozeb was determined in this study. All isolates were sensitive to difenoconazole, epoxiconazole, prothioconazole, tebuconazole, and cyproconazole (EC50 values ranged from 0.006 to 2.4 µg/ml). In contrast, 51% of the tested isolates were sensitive (EC50 values ranged from 0.003 to 0.2 µg/ml), and 49% were highly resistant (EC50 > 100 µg/ml) to carbendazim. Interestingly, all isolates were completely resistant to azoxystrobin, trifloxystrobin, and pyraclostrobin, and insensitive to boscalid, fluxapyroxad, and pydiflumetofen (EC50 > 100 µg/ml). The G143A mutation was detected in 82% (53) of the QoI‐resistant isolates and the E198A mutation in 97% (31) of the carbendazim‐resistant isolates. No apparent resistance mutations were detected in the succinate dehydrogenase genes (subunits sdhB, sdhC, and sdhD). Mancozeb completely inhibited mycelial growth of the isolates evaluated at a concentration of 100 µg/ml. All Argentinian Cercospora isolates were sensitive to the DMI fungicides tested, but we report for the first time resistance to QoI and MBC fungicides. Mechanism(s) other than fungicide target‐site modification may be responsible for resistance of Cercospora to QoI and MBC fungicides. Moreover, based on our results and on the recent introduction of SDHI fungicides on soybean in Argentina, Cercospora species causing CLB/PSS are insensitive (naturally resistant) to SDHI fungicides. Insensitivity must be confirmed under field conditions.

Pseudomonas fluorescens Showing Antifungal Activity against Macrophomina phaseolina, a Severe Pathogenic Fungus of Soybean, Produces Phenazine as the Main Active Metabolite

“…The M. phaseolina 2013-1 strain was obtained from infected soybean roots grown in Pergamino, Buenos Aires, Argentina, as previously reported [ 13 ]. Cercospora nicotianae isolate Cn_2017_BOL34 was obtained from soybean leaves with Cercospora leaf blight symptoms sampled from commercial soybean fields in Santa Cruz, Bolivia in 2017 as previously reported [ 15 ]. The strain 17-5-1 of Colletotrichum truncatum was isolated from soybean leaves with anthracnose symptoms sampled from commercial soybean fields in Roldán, Santa Fe, Argentina in 2017.…”

“…Fungi belonging to other genera such as Cercospora and Colletotrichum are causal agents of several diseases of soybean in Argentina and Brazil, which have also developed resistance or changes in sensitivity to commonly used fungicides [ 14 , 15 , 16 , 17 , 18 ].…”

Sensitivity assessment and SDHC‐I86F mutation frequency of Phakopsora pachyrhizi populations to benzovindiflupyr and fluxapyroxad fungicides from 2015 to 2019 in Brazil

“…The Kruskall–Wallis analysis of variance was used to assess differences among the EC 50 values to BZV and FXD, using R software 41 packages ‘ggplot2’ 42 and ‘rstatix’ 43 . The Kruskall–Wallis analysis was performed following the parameters described by Sautua et al 44 . Intrinsic activity was determined by the significant difference among EC 50 values for fungicides BZV and FXD.…”

Sensibilidad y resistencia a fungicidas de <i>Cercospora kikuchii</i>, agente causal del tizón de la hoja y mancha púrpura de la semilla de la soja

“…La distribución de especies de las principales BLAST hit de los genes codificante de proteínas predichos se muestra en la Figura 76. El borrador del genoma secuenciado se encuentra públicamente disponible en GenBank NCBI NIH con el número de acceso VTAY00000000 (Sautua et al, 2019b H a partir de Amaranthus hybridus (Sautua et al, 2020b).…”