Peronosporaceae Species Causing Downy Mildew Diseases of Poaceae, Including Nomenclature Revisions and Diagnostic Resources

Abstract

Downy mildew pathogens of graminicolous hosts (Poaceae) are members of eight morphologically and phylogenetically distinct genera in the Peronosporaceae (Oomycota, Peronosporales). Graminicolous downy mildews (GDMs) cause severe losses in 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. Thus, 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 a description 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, including DNA sequence data for types and/or voucher specimens, morphological features, and new illustrations. New sequence data for cox2 and 28S rDNA markers are provided from the type specimens of three species, Peronosclerospora philippinensis, Sclerospora iseilematis, and Sclerospora northii. Thirty-nine species of graminicolous downy mildews are accepted, and seven previously invalidly published taxa are validated. Fifty-five specimens are formally designated as types, including lectotypification of 10 species, neotypification of three species, and holotype designation for Sclerophthora cryophila.

Genome-Enabled Insights into Downy Mildew Biology and Evolution

“…within these six clades. Synteny with the complete genome of P. effusa was used to validate the derived chromosome-scale genome architectures of the DMP, Peronosclerospora sorghi (38), and the clade 5 hemibiotroph Phytophthora agathidicida (19). The extent of synteny with more diverse oomycetes, such as Phytophthora spp.…”

“…that have broad host ranges (52,79,127). Exceptions exist; for example, graminicolous DMPs are reported to be pathogenic on a wide variety of Poaceae (19,128). Also, the DMP Pseudoperonospora cubensis is pathogenic on more than 50 cucurbit species (106,111).…”

Synchrospora gen. nov., a New Peronosporaceae Genus with Aerial Lifestyle from a Natural Cloud Forest in Panama

“…Functionally, the synchronous production and ripening of up to more than 100 caducous sporangia per candelabra-like sporangiophore apex in S. medusiformis resembles 19 of the 20 DM genera [4,119,120,123,[125][126][127], allowing simultaneous aerial spread with high inoculum pressure. Another similarity between Synchrospora and the DMs is the small size (and hence weight) of the sporangia increasing their aerial dispersibility, whereas the unusually long, curved and twisted pedicels most likely facilitate sporangial clustering and adherence to plant surfaces as recently suggested for aerial long-pedicellate Phytophthora species [16].…”

“…Moreover, in several DM genera, the determinate sporangiophores also have dilated apices on which multiple sporangia or conidia are produced. These apices are saucer-shaped in Bremia, club-shaped in Eraphthora, cone-to club-shaped in Basidiophora and broad club-shaped to cylindrical in Baobabopsis [120][121][122][123]. However, none of the known DM genera form multifurcated candelabra-like sporangiophore apices.…”

Micromycetes associated with barley and their significance as pathogens in Russia

“…С середины 1960-х гг. были лишь единичные упоминания об обнаружении этого вида, обычно плохо задокументированные и непроверяемые (Crouch et al, 2022).…”