First Report of Tar Spot of Maize (Zea mays), Caused by Phyllachora maydis, in Ohio

Abstract

HomePlant DiseaseVol. 103, No. 7First Report of Tar Spot of Maize (Zea mays), Caused by Phyllachora maydis, in Ohio PreviousNext DISEASE NOTESFirst Report of Tar Spot of Maize (Zea mays), Caused by Phyllachora maydis, in OhioF. Dalla Lana, D. E. Plewa, E. S. Phillippi, D. Garzonio, R. Hesterman, N. M. Kleczewski, and P. A. PaulF. Dalla Lana†Corresponding author: F. Dalla Lana; E-mail Address: felipedallalana@gmail.comhttp://orcid.org/0000-0002-3112-6197Department of Plant Pathology, The Ohio State University, Wooster, OH, 44691Search for more papers by this author, D. E. PlewaDepartment of Crop Science, University of Illinois, Urbana, IL, 61801Search for more papers by this author, E. S. PhillippiDepartment of Crop Science, University of Illinois, Urbana, IL, 61801Search for more papers by this author, D. GarzonioGROWMARK, Inc., Bloomington, IL, 61701Search for more papers by this author, R. HestermanGROWMARK, Inc., Bloomington, IL, 61701Search for more papers by this author, N. M. Kleczewskihttp://orcid.org/0000-0001-5671-6727Department of Crop Science, University of Illinois, Urbana, IL, 61801Search for more papers by this author, and P. A. Paulhttp://orcid.org/0000-0002-7912-3067Department of Plant Pathology, The Ohio State University, Wooster, OH, 44691Search for more papers by this authorAffiliationsAuthors and Affiliations F. Dalla Lana1 † D. E. Plewa2 E. S. Phillippi2 D. Garzonio3 R. Hesterman3 N. M. Kleczewski2 P. A. Paul1 1Department of Plant Pathology, The Ohio State University, Wooster, OH, 44691 2Department of Crop Science, University of Illinois, Urbana, IL, 61801 3GROWMARK, Inc., Bloomington, IL, 61701 Published Online:14 May 2019https://doi.org/10.1094/PDIS-01-19-0070-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat In October 2018, maize (Zea mays L.) leaf samples with symptoms commonly associated with tar spot were received from Hancock, Wyandot, Fulton, Clark, Van Wert, and Crawford Counties in Ohio. Disease severity on individual leaves ranged from <1 to 10%, depending on the hybrid and location. Lesions were black, raised, and rounded, and ranged in size from 0.9 to 3.93 mm by 0.72 to 2.0 mm (n = 40, average 2.28 by 1.38 mm). A few of the lesions (<1%) presented a tan halo surrounding the black spot, resembling the fisheye lesions often considered typical of tar spot. Microscopic observations of leaf pieces sectioned through lesions showed ascomata occurring singly or in groups within a clypeus. Ascomata contained cylindrical asci with hyaline, aseptate, ellipsoid ascospores, ranging in size from 5.0 to 7.5 by 7.5 to 13.75 µm (n = 40, average 5.9 by 10.9 µm), and filiform paraphyses. Based on symptoms and fungal morphology, the disease was identified as tar spot and the pathogen as Phyllachora maydis Maubl. For molecular confirmation, DNA was extracted from ascomata on leaf samples from Hancock County, and amplicons of the internal transcribed spacer regions were generated using primers ITS5 and ITS4 (White et al. 1990). The results confirmed the fungus as P. maydis, showing 97% sequence homology to GenBank deposit accession MG881848.1 (McCoy et al. 2018), with 100% query cover, max score of 830, and E value of 0.0. Because P. maydis is an obligate biotroph (Müller and Samuels 1984), and as such nonculturable (Ruhl et al. 2016), Koch’s postulates were not attempted. The sequence from Hancock County was deposited in GenBank (accession no. MK184990). Although previously reported in the United States in Indiana, Illinois, Florida, Iowa, Michigan, and Wisconsin (McCoy et al. 2018; Ruhl et al. 2016), tar spot is still an emerging disease in the United States for which the economic impact is unknown. However, there have been reports of significant yield loss in Illinois, Indiana, Michigan, and Wisconsin in 2018 (N. M. Kleczewski, personal communication). It has been suggested that significant losses occur in Central and South America when plants are coinfected with P. maydis and Monographella maydis (Mottaleb et al. 2018). The latter species has not been reported in the United States, but evidence from preliminary studies indicates that P. maydis alone may be capable of impacting grain yield (N. M. Kleczewski, personal communication).The author(s) declare no conflict of interest.