Current understanding of the genetic and molecular interactions between the tar spot pathogen Phyllachora maydis and maize

Authors: ROGERS, ABIGAIL - Purdue University; Jaiswal, Namrata; CALDWELL, DENISE - Purdue University; ROGGENKAMP, EMILY - Michigan State University; Scofield, Steven; CHILVERS, MARTIN - Michigan State University; IYER-PASCUZZI, ANJALI - Purdue University; Helm, Matthew

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Corn (maize) is one of the most important crops grown in the United States, but in recent years it has been increasingly damaged by a fungal disease called tar spot. This disease is caused by a fungus named Phyllachora maydis, which has spread rapidly across U.S. corn-growing regions since it was first detected in 2015. Tar spot can seriously reduce crop yields, costing U.S. farmers billions of dollars, yet scientists still know relatively little about how this fungus infects corn or how corn plants try to defend themselves. In this peer-reviewed manuscript, we present the first comprehensive and detailed understanding of the biological interactions between corn and this pathogen. Importantly, this manuscript is also the first to present a working model, based on experimental data, describing how Phyllachora maydis infects corn leaves and spreads within the plant. Specifically, this fungus infects corn by breaking through the leaf surface, grows inside the soft inner leaf tissue, and forms small black structures that release infection particles that, in turn, start new infections. By clarifying how tar spot develops and how resistance may work, this manuscript provides critical knowledge that will help guide researchers to develop better disease-resistant corn varieties and improve management strategies. This work directly supports U.S. agriculture by helping protect corn yields, farm profitability, and long-term food security.

Technical Abstract: Since its initial detection in Indiana and Illinois in 2015, Phyllachora maydis has rapidly emerged as a significant constraint to maize (Zea mays) production in continental North America. Over the past decade, this ascomycete fungal pathogen has caused recurrent epidemics of tar spot disease throughout maize-growing regions across the United States and Canada, frequently resulting in substantial yield losses. Notably, in 2024, tar spot disease was responsible for an estimated economic yield loss of $1.37 billion to U.S. farmers. Despite its agronomic impact to United States agriculture, no definitive sources of genetic resistance to P. maydis have been identified in maize germplasm, underscoring a critical need to elucidate the molecular and genetic basis of disease resistance. Recent studies have begun to investigate the genetic, molecular, and cellular mechanisms underlying P. maydis virulence and host colonization with the long-term goal of developing durable resistance strategies. In this review, we synthesize the latest advances in our understanding of host-pathogen interactions within the maize - P. maydis pathosystem with a focused emphasis on the genetic, molecular, and cellular dynamics that shape these interactions. Building on these insights, we outline key knowledge gaps and propose future research priorities aimed at accelerating the development of durable resistance and effective disease management strategies. Given the significant agricultural impact of P. maydis, coupled with its continued geographical expansion, we propose this fungal pathogen poses an emerging threat to global maize production and emphasize the necessity for sustained research efforts to improve host resistance and disease management strategies.