Characterization of cytochrome b from European field isolates of Cercospora beticola with quinone outside inhibitor resistance

Abstract

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most important foliar disease of sugar beet worldwide. Control strategies for CLS rely heavily on fungicides including quinone outside inhibitor (Q O I) fungicides. We collected 866 C. beticola isolates from sugar beet growing regions in France and Italy and assessed their sensitivity to the Q O I fungicide pyraclostrobin. To gain an understanding of the molecular basis of Q O I resistance, we cloned the full-length coding region of Cbcytb. All tested Q O I-resistant isolates harbored a point mutation in Cbcytb at nucleotide position 428 that conferred an exchange from glycine to alanine at amino acid position 143 (G143A). A PCR assay was developed to discriminate Q O Isensitive and Q O I-resistant isolates based on the G143A mutation. Our results indicate that Q O I resistance has developed in some European C. beticola populations in Italy and monitoring the G143A mutation is an essential fungicide resistance management strategy. I would also like to thank Viviana Rivera-Varas for her work towards this study and without whom this study would not have been possible. I also want to thank my lab mates, Xiaoyun Wang and Kurt Rudolph, for their guidance and assistance in several of my laboratory techniques and experiments. Most importantly, I am indebted to my family for their unconditional love, encouragement, and support. Lastly, I would like to thank God for making everything smooth and possible for me. v

Occurrence of the F129L mutation in Alternaria solani populations in Germany in response to QoI application, and its effect on sensitivity

“…According to Birla et al . () in Cercospora beticola , QoI resistance developed independently at several geographical regions. Kim et al .…”

“…As some of the sampling locations are relatively far apart from each other (c. 180 km), the F129L mutations may have arisen independently. According to Birla et al (2012) in Cercospora beticola, QoI resistance developed independently at several geographical regions. Kim et al (2003) noted that QoI resistance in Pyricularia grisea occurred in five genetic backgrounds.…”

First report of G143A strobilurin resistance in Cercospora beticola in sugar beet (Beta vulgaris) in Poland

“…The QoI resistance is usually conferred by single-point mutation in mitochondrial cytochrome b gene (cytb). Amino acid exchange from glycine to alanine at the 143 codon position (G143A) was detected as the main source of QoI resistance in many plant pathogenic fungi (Birla et al 2012;Bolton et al 2012;Jiang et al 2009;Obuya and Franc 2016). Substitution phenylalanine to leucine (F129L) and glycine to arginine (G137R) are less common (Fisher and Meunier 2008).…”

“…There were no reports on QoI field resistance in the USA and Greece until 2011, and in France until 2012 (Birla et al 2012;Malandrakis et al 2011;Secor et al 2010). The first QoI-resistant isolates of C. beticola containing the substitution of glycine to serine at the 143 codon position (G143S) and others were detected under artificial conditions only (Malandrakis et al 2006).…”

“…However, due to the widespread use of strobilurin in CLS management QoI resistance is developing rapidly in many sugar beet growing areas. Nowadays QoI-resistant field isolates of C. beticola with the G143A mutation have been detected in many sugar beet growing areas in Europe (mostly the Mediterranean area) and the USA Birla et al 2012;Obuya and Franc 2016). Recently the F129L mutation was identified as a moderate source of QoI resistance in C. beticola isolates obtained from table beets in the USA (New York) (Vaghefi et al 2016).…”