Host Response of Winter Wheat to the Causal Agents of Eyespot and Fungicide Resistance of the Pathogens

Eyespot is one of the most important fungal diseases of wheat in the Czech Republic. As part of a long-term study (2015–2024), the occurrence, population structure, and pathogenic variability of Oculimacula yallundae and Oculimacula acuformis were investigated. In total, 356 O. yallundae, 24 O. acuformis, and 33 mixed cultures were collected and identified using PCR. The study also included small-plot inoculation trials (2022–2023) to assess the response of widely grown winter wheat cultivars. Disease severity was evaluated visually, pathogen DNA was quantified using qPCR, and the presence of the resistance gene Pch1 was determined with the STS marker Xorw1. In addition to these analyses, monitoring of fungicide resistance to two commonly used fungicides (fluxapyroxad and prothioconazole) was performed. The results showed significant differences among cultivars and seasons. Genotypes carrying Pch1—including Annie, Campesino, Illusion, KWS Donovan, LG Absalon, and Pallas—exhibited the lowest levels of infection, whereas Mercedes and Dagmar were the most susceptible. The qPCR reliably detected and distinguished both pathogens, with O. yallundae occurring at higher concentrations. Fungicide sensitivity testing revealed EC50 values (mean ± SD) of 0.09 ± 0.13 μg·mL−1 for fluxapyroxad and 0.30 ± 0.22 μg·mL−1 for prothioconazole, indicating that eyespot pathogens remain largely sensitive, with only minor signs of reduced sensitivity.