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ARS Home » Midwest Area » Wooster, Ohio » Corn, Soybean and Wheat Quality Research » Research » Publications at this Location » Publication #417486
Research Project: Detection and Characterization of Genetic Resistance to Corn and Soybean Viruses

Location: Corn, Soybean and Wheat Quality Research

Title: Characterization of three resistance-breaking isolates of sugarcane mosaic virus from Rwanda and implications for maize lethal necrosis

Author
item Wilson, Jennifer - Jenny
item Willie, Kristen
item STEWART, LUCY - Former ARS Employee
item REDINBAUGH, MARGARET - The Ohio State University
item Ohlson, Erik

Submitted to: bioRxiv
Publication Type: Pre-print Publication
Publication Acceptance Date: 7/24/2024
Publication Date: 7/24/2024
Citation: Wilson, J.R., Willie, K.J., Stewart, L.R., Redinbaugh, M.G., Ohlson, E.W. 2024. Characterization of three resistance-breaking isolates of sugarcane mosaic virus from Rwanda and implications for maize lethal necrosis. bioRxiv. 2024.07.23.604352.. https://doi.org/10.1101/2024.07.23.604352.
DOI: https://doi.org/10.1101/2024.07.23.604352

Interpretive Summary: Maize lethal necrosis is a deadly disease of maize caused by synergy between two, co-infecting viruses: maize chlorotic mottle virus (MCMV) and a potyvirus, most often sugarcane mosaic virus (SCMV). This disease causes major losses in corn production in many regions of the world, especially in East Africa. The main way that farmers combat maize lethal necrosis is through growing virus resistant corn lines. We discovered that three variants of SCMV from Rwanda can overcome the three most widely used potyvirus resistance genes, infecting virus resistant corn lines that normally cannot be infected by this virus. This discovery raises concerns considering that these three resistance genes are widely used in corn cultivars grown worldwide. Fortunately, these variants of SCMV did not cause more severe disease when plants were co-infected with the second virus, MCMV. Plants carrying two or more of the potyvirus resistance genes had significantly less severe disease than corn without these genes, and avoided the worst disease outcomes, such as plant death, even when infected with the more severe SCMV variants. These results reveal a potential reason why epidemics of this disease have been so severe in Rwanda and other East African countries where corn hybrids carry only a single potyvirus resistance gene. This study highlights the importance of incorporating multiple sources of virus resistance into corn lines when breeding for MLN resistance and serves as useful information to breeders. Ultimately, the development of durable host resistance to MLN will greatly benefit farmers who have been combating this deadly disease.

Technical Abstract: Maize lethal necrosis (MLN) is a devastating disease of maize caused by synergy between two viruses: maize chlorotic mottle virus (MCMV) and a potyvirus, most often sugarcane mosaic virus (SCMV). Throughout the 2010s, severe MLN outbreaks occurred in sub-Saharan East Africa including Kenya, Rwanda, and Ethiopia. In this study, we assessed the virulence of SCMV isolates collected from Rwanda by screening a panel of maize near isogenic lines containing different combinations of major potyvirus resistance loci. We discovered that the three Rwandan SCMV isolates tested could overcome all three potyvirus resistance loci even when used in combination, including one isolate that could asymptomatically infect all resistant lines tested. To understand how SCMV virulence may contribute to MLN, each of the three isolates were co-inoculated with MCMV on a panel of SCMV and MCMV resistant maize lines. No significant differences in MLN severity were observed for the Rwandan isolates compared to the reference SCMV isolates, indicating that increased virulence in SCMV single infection does not necessarily correlate with increased MLN severity in co-infection with MCMV. For all SCMV isolates tested, at least two potyvirus resistance loci were needed to reduce MLN severity, and maize lines with a combination of SCMV and MCMV resistance were most effective. Surprisingly, in some cases co-infection with MCMV facilitated SCMV infection of potyvirus resistant lines that SCMV could not infect alone. These results underscore the challenges of developing durable MLN resistance and highlight the importance of incorporating strong, multigenic potyvirus resistance into MLN resistance breeding programs.