Current Understanding of the Genetic and Molecular Interactions Between the Tar Spot Pathogen <i>Phyllachora maydis</i> and Maize

Since its initial detection in Indiana and Illinois in 2015, tar spot of maize, caused by <i>Phyllachora maydis</i>, has rapidly emerged as a significant constraint to maize (<i>Zea mays</i>) production in the continental United States. Over the past decade, this pathogen has caused recurrent disease epidemics throughout maize-growing regions across the United States and Canada, causing substantial yield losses. Notably, in 2024, tar spot 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 <i>P. maydis</i> have been identified in maize germplasm, underscoring a critical need to elucidate the molecular and genetic basis of disease resistance. Accordingly, recent studies have begun to investigate the genetic, molecular, and cellular mechanisms underlying <i>P. maydis</i> 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 - <i>P. maydis</i> 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 <i>P. maydis</i>, 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.