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POSTERS: New and emerging diseases

Tar Spot of Corn: Distinguishing the fungal communities of tar spot and fish-eye symptoms through amplicon sequencing
Emily Roggenkamp - Michigan State University. Reid Longley- Michigan State University, Martin Chilvers- Michigan State University, Gregory Bonito- Michigan State University, Austin Mccoy- Michigan State University, Rebecca Shay- Michigan State University, Zachary Noel- Michigan State University, Mali

Tar spot is a fungal disease complex of corn that has been destructive and yield limiting in Central and South America for nearly 50 years. Phyllachora maydis, the causal agent of tar spot, is an emerging corn pathogen in the United States. The tar spot disease complex putatively includes Monographella maydis (syn. Microdochium maydis), which increases disease damage through the development of necrotic halos surrounding tar spot lesions. These necrotic halos, termed “fish-eye” symptoms, have been identified in the United States, though Monographella maydis has not yet been confirmed. In this study, next-generation sequencing of the internal transcribed spacer-1 (ITS1) ribosomal DNA was used to identify fungal taxa that distinguish tar spot infections with or without fish-eye symptoms. Fungal communities within tar spot only lesions were significantly different from communities within fish-eye lesions. Interestingly, a single OTU was found to be significantly more abundant in fish-eye lesions compared to tar spot lesions. This OTU was positively associated with fish-eye symptom networks, but not in tar spot symptom networks. Many OTUs identified as Phyllachora maydis, suggesting that different isolate genotypes may be capable of causing both tar spot and fish-eye symptoms, independent of other fungi. We conclude that Monographella maydis is not required for fish-eye symptoms in tar spot of corn in Michigan.