Fungicide Resistance in Cercospora kikuchii, a Soybean Pathogen

Abstract

Isolates of Cercospora kikuchii, a soybean (Glycine max) pathogen causing Cercospora leaf blight and purple seed stain, were tested to determine baseline sensitivities (n = 50) to selected quinone outside inhibitor (QoI) fungicides by conducting radial growth assays on fungicide-amended media. Baseline effective fungicide concentration to inhibit 50% of fungal radial growth (EC50) values were compared with EC50 values for isolates collected in 2011 (n = 50), 2012 (n = 50), and 2013 (n = 36) throughout soybean-producing areas in Louisiana. Median EC50 values for isolates subjected to QoI fungicides were significantly (P = 0.05) higher across all 3 years. Cross-resistance to QoI fungicides was observed in resistant isolates collected in 2011 to 2013. Discriminatory doses were developed for QoI fungicides to distinguish between sensitive and resistant isolates. On average, 89% of all isolates screened in 2011 to 2013 were resistant to QoI fungicides. At a discriminatory dose of thiophanate methyl (TM), a methyl benzimidazole carbamate (MBC) fungicide, at 5 μg/ml, resistance was detected in the 2000, 2011, 2012, and 2013 collections at 23, 38, 29, and 36%, respectively. Isolates exhibiting multiple resistance to QoI fungicides and TM also were detected in 2011, 2012, and 2013 at frequencies of 34, 26, and 31%, respectively. Based on these results, Cercospora leaf blight management strategies in Louisiana using solo applications of QoI or MBC fungicides in soybean should be reconsidered.

In vitro sensitivity assessment of late season soybean pathogens to fungicide mixtures

“…These EC 50 values are more likely to occur biologically and are similar to previous reports from the literature (Price et al 2015;Batzer et al 2016). In the present study, for two of the three fungi analyzed (C. kikuchii and P. phaseoli), the W1.4 model provided the lowest EC 50 .…”

“…It is necessary to create a fungicide sensitivity-testing program in Argentina due to the numerous cases of fungicide resistance that have been already reported worldwide in soybean. In the United States, C. kikuchii isolates exhibiting multiple resistance to QoI and benzimidazole fungicides have already been confirmed and reported (Price et al 2015).…”

Perspectives and Challenges for Sustainable Management of Fungal Diseases of Mungbean [Vigna radiata (L.) R. Wilczek var. radiata]: A Review

“…However, disease management failures in legume crops associated with fungicide resistance have been reported from several countries (Chang et al, 2007;Lonergan et al, 2015;Price et al, 2015). For example, Price et al (2015) reported that isolates of C. kikuchii (Cercospora leaf spot) from soybean fields in Louisiana State, USA were insensitive to thiophanate methyl.…”

“…However, disease management failures in legume crops associated with fungicide resistance have been reported from several countries (Chang et al, 2007;Lonergan et al, 2015;Price et al, 2015). For example, Price et al (2015) reported that isolates of C. kikuchii (Cercospora leaf spot) from soybean fields in Louisiana State, USA were insensitive to thiophanate methyl. Isolates of Ascochyta rabiei (ascochyta blight of chickpea) from Canada and USA showed insensitivity with fungicides pyraclostrobin, chlorothalonil, fluxapyroxad, and prothioconazole (Chang et al, 2007;Lonergan et al, 2015).…”

“…In addition, farmers do not commonly rotate fungicides with different mode of actions due to poor knowledge and extension on IPM. As fungicides resistance is a big concern for legume industry in several countries (Chang et al, 2007;Lonergan et al, 2015;Price et al, 2015), the problem may arise in mungbean industry. Fungicide resistance could be significant challenge for the mungbean farmers in future to manage diseases effectively.…”