Peronosporaceae species causing downy mildew diseases of Poaceae, including nomenclature revisions and diagnostic resources

Authors: Crouch, Jo Anne; DAVIS, WILLIAM - Orise Fellow; Shishkoff, Nina; CASTROAGUDIN, VANINA - Oak Ridge Institute For Science And Education (ORISE); Martin, Frank; MICHELMORE, RICHARD - University Of California; THINES, MARCO - Goethe University

Submitted to: Fungal Systematics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2022
Publication Date: 4/8/2022
Citation: Crouch, J.A., Davis, W.J., Shishkoff, N., Castroagudin, V.L., Martin, F.N., Michelmore, R., Thines, M. 2022. Peronosporaceae species causing downy mildew diseases of Poaceae, including nomenclature revisions and diagnostic resources. Fungal Systematics and Evolution. 9(1):43-86. https://doi.org/10.3114/fuse.2022.09.05.
DOI: https://doi.org/10.3114/fuse.2022.09.05

Interpretive Summary: Downy mildews cause severe losses to cereal crops such as maize, millets, sorghum, and sugarcane in many parts of the world, especially in tropical climates. Some foreign downy mildews pose a high-risk to U.S. agriculture due to their ability to cause significant losses in staple food crops such as corn. Better tools and resources to accurately identify cereal downy mildews are needed to reduce the risk of these pathogens entering the U.S. In this research, we conducted an analysis of all known information available for the cereal downy mildews, identified knowledge gaps, and addressed several outstanding taxonomic and nomenclature issues that hindered accurate pathogen identification. A comprehensive set of identification tools and resources was developed, including new DNA sequence data and standardized illustrations of pathogen morphological features. These resources will provide an important source of information for plant disease diagnosticians, regulatory officials, plant pathologists, extension personnel and growers that will facilitate early and accurate pathogen identification and to minimize the spread and impact of cereal downy mildew diseases.

Technical Abstract: Downy mildew pathogens of graminicolous hosts (Poaceae) are members of eight phylogenetically diverse genera in the Peronosporaceae (Oomycota, Peronosporales). Graminicolous downy mildews cause severe losses to crops such as maize, millets, sorghum, and sugarcane in many parts of the world, especially in tropical climates. In countries where the most destructive GDMs are not endemic, these organisms are often designated as high-risk foreign pathogens and subject to oversight and quarantine by regulatory officials. As such, there is a need to reliably and accurately identify the causal organisms. This paper provides an overview of the Peronosporaceae species causing graminicolous downy mildew diseases, with overviews of their impact on agriculture and the environment, along with brief summaries of the nomenclatural and taxonomic issues surrounding these taxa. Key diagnostic characters are summarized and illustrated, including morphological features and DNA sequence data for types and/or voucher specimens. New sequence data for cox2 and 28S rDNA markers are provided from the type specimens of three species, including Peronosclerospora philippinensis and the first ever molecular data for Sclerospora iselematis and S. northii. Twenty-eight species are accepted, including validation of seven previously invalid taxa. Forty-one specimens are formally designated as types, including lectotypification of ten species, neotypification of three species, and holotype designation for Sclerophthora cryophila.