Taxonomy, diversity, and effects of viruses infecting Phytophthora spp.

Phytophthora species are among the most destructive oomycete plant pathogens, responsible for substantial agricultural losses worldwide. Compared with fungi, oomycetes remain relatively understudied, and to date, only eight Phytophthora species have been investigated for the presence of viruses. In fungi, viral infections are known to induce hypo- or hypervirulence, stimulating extensive research aimed at identifying mycoviruses with potential as biological control agents. Recent advances in bioinformatics and next-generation sequencing (NGS) technologies have markedly enhanced the detection of viruses in both fungi and oomycetes, even when present at low titres. Notably, no DNA viruses have yet been reported to infect fungi or oomycetes. This review presents a comprehensive update on the taxonomic status of viruses associated with Phytophthora, based on the latest ICTV classification (MSL 40, v2). Most reported viruses belong to the classes Bunyaviricetes and the family Pseudototiviridae. We synthesize current knowledge of all viruses identified in Phytophthora, together with their documented effects on the host. This consolidated information provides a strategic foundation for developing integrated disease management approaches targeting Phytophthora. Importantly, we highlight critical research gaps, including limited studies on transmission biology, insufficient molecular characterization of host–virus interactions, and the lack of field-level validation of virus-mediated hypovirulence. Addressing these gaps is essential to translate existing knowledge into practical applications for sustainable disease management.