Virulence and molecular characterization of Blumeria graminis isolates from wheat fields across Ontario

Authors: LIU, MIAO - Agriculture And Agri-Food Canada; LIM, SEARA - Agriculture And Agri-Food Canada; SHOUKOUHI, PARIVASH - Agriculture And Agri-Food Canada; XUE, ALLEN - Agriculture And Agri-Food Canada; CHEN, YUANHONG - Agriculture And Agri-Food Canada; BURT, ANDREW - Agriculture And Agri-Food Canada; HUMPHREYS, GAVIN - Agriculture And Agri-Food Canada; Cowger, Christina; SERAJAZAR, MITRA - University Of Guelph; MCCALLUM, BRENT - Morden Research And Development Centre

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2025
Publication Date: 4/2/2025
Citation: Liu, M., Lim, S., Shoukouhi, P., Xue, A.G., Chen, Y., Burt, A.J., Humphreys, G., Cowger, C., Serajazar, M., Mccallum, B. 2025. Virulence and molecular characterization of Blumeria graminis isolates from wheat fields across Ontario. Canadian Journal of Plant Pathology. https://doi.org/10.1080/07060661.2025.2475813 .
DOI: https://doi.org/10.1080/07060661.2025.2475813

Interpretive Summary: In Ontario, Canada, the frequency and severity of powdery mildew caused by Blumeria graminis on wheat has been increasing recently. It’s important to continue monitoring how effective wheat resistance genes are against this pathogen. In 2021 and 2022, 74 isolates or strains of B. graminis were created from wheat samples collected from 40 randomly selected fields and greenhouses in Ontario. These samples were then tested on 24 individual wheat mildew resistance genes, each in a different wheat line. Compared to a previous survey in 2018 – 2019, the virulence frequencies to most resistance (Pm) genes have increased over the years, including Pm1a, Pm1b, Pm1c, Pm2, Pm3a, Pm3f, Pm5a, Pm5d, Pm17, Pm30, Pm34, Pm35, Pm43, M1AG12, and NCAG13. Nevertheless, Pm12, Pm16, Pm21, and Pm37 each remained effective against all mildew isolates. Also, nine genes (Pm1a, Pm1b, Pm1c, Pm3d, Pm4b, Pm25, Pm29, MlAG12, and NCAG13) were generally effective, with resistance to more than 80% of the isolates. The remaining 11 genes were ineffective. Analyses of genetic data showed no geographic subdivision of the sampled isolates, suggesting the B. graminis population mixes throughout the sampled area.

Technical Abstract: In Ontario, Canada, the prevalence and severity of the powdery mildew (PM) caused by Blumeria graminis on wheat has been escalating during the recent decades. Continual monitoring the effectiveness of PM-resistance genes (Pm) and the pathogen virulence spectrum in the field is essential for breeding durable resistance to control the diseases. In 2021 and 2022, 74 single colony isolates of B. graminis were purified from field samples collected from 40 randomly selected wheat fields and greenhouses in Ontario, then tested for virulence on 24 single-Pm gene wheat lines. Compared to a previous survey in 2018 – 2019, the virulence frequencies to most Pm have increased over the years, including Pm1a, Pm1b, Pm1c, Pm2, Pm3a, Pm3f, Pm5a, Pm5d, Pm17, Pm30, Pm34, Pm35, Pm43, M1AG12, and NCAG13. Nevertheless, Pm12, Pm16, Pm21, and Pm37 each remained effective against all isolates. Nine genes (Pm1a, Pm1b, Pm1c, Pm3d, Pm4b, Pm25, Pm29, MlAG12, and NCAG13) were generally effective, with resistance to more than 80% of the isolates. The remaining 11 genes were ineffective, having susceptible reactions to 37 – 97 % of the isolates. DNA sequences of 116 isolates (2018 – 2022) for the fragments of alternative oxidase (AOX), protein kinase A (PKA), protein phosphatase type 2A (PPA) and ß-tubulin (bTUB) genes resulted in only four informative segregating single nucleotide polymorphisms (SNPs). The linkage disequilibrium analyses of these four SNPs suggested the frequent genetic recombination. Additionally, network analyses of VP data showed no genetic subdivision, suggesting B. graminis in the sampled area is likely a panmictic population.