Tar spot of corn has been a major foliar disease in several Latin American countries since 1904. In 2015, tar spot was first documented in the United States and has led to significant yield losses of approximately 4.5 million t. Tar spot is caused by an obligate pathogen, Phyllachora maydis, and thus requires a living host to grow and reproduce. Due to its obligate nature, biological and epidemiological studies are limited and impact of disease in corn production has been understudied. Here we present the current literature and gaps in knowledge of tar spot of corn in the Americas, its etiology, distribution, impact and known management strategies as a resource for understanding the pathosystem. This will in tern guide current and future research and aid in the development of effective management strategies for this disease.
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, first reported in 2015 from major
corn producing regions of the country. 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. A
recent surge in disease severity and loss of yield attributed to tar spot in the
United States has led to increased attention and expanded efforts to understand
the disease complex and how to manage it. 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 having fish-eye symptoms. Two low
abundance OTUs were identified as Microdochium sp., however,
neither were associated with fish-eye symptom development. Interestingly, a
single OTU was found to be significantly more abundant in fish-eye lesions
compared to tar spot lesions and had a 91% ITS1 identity to
Neottiosporina paspali. In addition, the occurrence of this
OTU was positively associated with Phyllachora maydis fish-eye
symptom networks, but not in tar spot symptom networks. Neottiosporina
paspali has been reported to cause necrotic lesions on various
monocot grasses. Whether the related fungus we detected is part of the tar-spot
complex of corn and responsible for fish-eye lesions remains to be tested.
Alternatively, 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.