Presence and prevalence of Ramularia collo-cygni SDHI resistance in Irish barley seed

Ramularia leaf spot of barley, caused by Ramularia collo-cygni has become a serious disease threat to barley production. By inducing necrotic lesions, the disease expiates the onset of leaf senescence, which can result in significant grain yield and quality losses. In addition to surviving between seasons in trash, stubble and volunteers, R. collo-cygni can be transmitted from seed to emerging seedlings. As a potential additional means of transmission it may also pose a risk for the spread of specific traits such as fungicide resistance. In the present study, we screened Irish barley seed stocks harvested in the years 2015–2017 for the presence of R. collo-cygni using qPCR, and subsequently using an amplicon sequencing assay screened for the presence of alleles in the SDHC gene of R. collo-cygni associated with SDHI resistance. Over the three year period > 60% of the samples screened had detectable levels of R. collo-cygni present. In a subsample of these five alleles associated with resistance (SDHC—N87S, G91R, H145R, R152M and H153R) were detected. The prevalence of the key alleles C-N87S and C-H146R remained stable over the three year period, and was similar to that detected amongst an isolate collection established in 2022.