Frequency of a mutant allele of cytochrome b conferring resistance to Ool fungicides in the Czech population of Ramularia collo-cygni

Ramularia collo-cygni (RCC) is a fungal pathogen infecting both spring and winter barley and causing Ramularia leaf spot (RLS). Fungicides based on strobilurin initially provided one of the best chemical solutions to manage the disease, but resistance in RCC to strobilurin developed quickly. In strobil-urin-resistant RCC isolates, a single point mutation is present in the cytochrome b gene. A population of 302 single-spore isolates of RCC, all collected in the Czech Republic in 2009, was analysed using a CAPS marker. The A143 (strobilurin resistant) allele was found in 47% of the isolates. Frequency of the mutant allele was significantly affected by the application frequency of strobilurin fungicides. In locations with more frequent application of strobilurins, the frequency of the allele A143 in RCC isolates was higher (up to 100%). By contrast, in locations where strobilurin fungicides were not used the mutant allele occurred only in 0-5% of the isolates.