Is Microdochium maydis Associated with Necrotic Lesions in the Tar Spot Disease Complex? A Culture-Based Survey of Maize in Mexico and the Midwestern United States

Abstract

Tar spot, caused by  Phyllachora maydis, is an emerging disease of corn in the United States. Stromata of  P. maydis are sometimes surrounded by necrotic lesions known as fisheyes and were previously reported to be caused by the fungus Microdochium  maydis. The association of  M. maydis with fisheye lesions has not been well documented outside of initial descriptions from the early 1980s. The objective of this work was to assess and identify Microdochium-like fungi associated with necrotic lesions surrounding P. maydis stromata using a culture-based method. In 2018, corn leaf samples with fisheye lesions associated with tar spot stromata were collected from 31 production fields across Mexico, Illinois, and Wisconsin. Cultures of pure isolates collected from Mexico believed to be M. maydis were included in the study. A total of 101 Microdochium/ Fusarium-like isolates were obtained from the necrotic lesions, and 91% were identified as  Fusarium spp., based on initial ITS sequence data. Multi-gene (ITS, TEF1-α, RPB1, and RPB2) phylogenies were constructed for a subset of 55 isolates;  Microdochium,  Cryptostroma, and  Fusarium reference sequences were obtained from GenBank. All the necrotic lesion isolates clustered within  Fusarium lineages and were phylogenetically distinct from the Microdochium clade. All Fusarium isolates from Mexico belonged to the  F. incarnatum-equiseti species complex, whereas >85% of the U.S. isolates grouped within the  F. sambucinum species complex. Our study suggests that initial reports of M. maydis were misidentifications of resident Fusarium spp. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .