Fungicide strategies and resistance of Ramularia collo-cygni to demethylation and succinate dehydrogenase inhibitors in Austrian winter barley (Hordeum vulgare)

Abstract

Ramularia collo-cygni B. Sutton and J.M. Waller is a major disease in Austrian barley-growing regions. To date, fungicide application is the most effective method to manage the disease; however, fungicide resistance to demethylation and succinate dehydrogenase inhibitors has developed over the last few years. In the growing seasons 2016/2017 and 2017/2018, field trials were carried out to analyze the efficiency of fungicide strategies based on different fungicide classes. Disease development, growth parameters and monitoring of CYP51 and sdh mutations were determined. Fungicide treatments resulted in higher disease control, green leaf area and grain yield. In Austrian R. collo-cygni field populations, the frequency of the mutations CYP51-I325T and CYP51-I328L was low to moderate. Frequency of mutations sdhC-H146R and sdhC-H153R was low. Frequencies of CYP51-I325T and -I328L were similar and increased following DMI application. Frequency of sdhC-H146R was higher compared to sdhC-H153R. The SDHI benzovindiflupyr showed a higher selection rate for sdh mutations compared to bixafen. These sdh mutations were not selected if chlorothalonil was used as mixing partner, leading to a stable composition of sdh resistance alleles over the last two years. Chlorothalonil was proven to be an effective tool for anti-resistance strategies. Currently, SDHIs and DMIs are the backbone of Ramularia leaf spot control in Austria; however, the level of resistance is likely to increase in absence of suitable anti-resistance strategies and following the ban of chlorothalonil.

Fungicide Resistance Evolving in Ramularia collo-cygni Population in Estonia

“…As a result, DMIs are regarded as being ineffective against R. collo-cygni in these countries [ 48 ]. Intensive monitoring of barley fields by Syngenta demonstrated that DMI field efficacy against RLS decreased from nearly 100% in 2014 to around 30% in 2019 [ 49 ]. The reduction in the control of R. collo - cygni by DMIs has increased concerns for future management of RLS [ 35 ].…”

Detection of Ramularia collo-cygni DMI- and SDHI-resistant field populations in Austria and the effect of fungicides on the population and genetic diversity

“…The qPCR was established in Syngenta Resistance Centre in Stein, Switzerland. PCR assays were done according to the method described by Assinger et al (2021).…”