Modern Taxonomy as the Foundation for Identifying and Managing Fungal and Fungus-Like Plant Pathogens

Reliable, up-to-date fungal and oomycete taxonomy underpins every aspect of plant pathology by enabling accurate pathogen identification, robust host-range analyses, clear assessment of geographic spread, and the development of effective disease management strategies. Yet, despite major advances in systematics and molecular phylogenetics, the integration and use of current names in applied plant pathology remains inconsistent. We discuss best practices for accurate identification, combining morphology, molecular data, and phylogenetic frameworks, and examine challenges arising from the use of informal or unofficial terms such as forma specialis. We outline formally recognized designations that can be used in lieu of forma specialis, such as the rank forma, which is governed by the International Code of Nomenclature for algae, fungi and plants and provides a more precise and reproducible means for describing variation below the species level. We use case studies of phytopathologically important fungi and oomycetes to illustrate recurring challenges, including misidentifications, species complexes, cryptic species, and pathogens with highly complex life cycles. We also provide practical guidance for nonexperts on how to navigate competing taxonomic concepts in their work. Finally, we outline a practical workflow for identifying plant pathogenic fungi and oomycetes to strengthen the link between taxonomy and plant pathology, incorporating curated databases, the deposition of voucher specimens, and collaboration between systematists and pathologists. In applied plant pathology, taxonomy and nomenclature are not merely academic concerns; researchers generate the correct identifications and reference data that diagnosticians, extension personnel, and industry translate into reliable diagnostics, fungicide efficacy and resistance management, regulatory information, and economically efficient disease management.