Revisiting fosetyl-Al: mechanisms, systemic behavior and its role as a host-driven tool in integrated management of soil-borne oomycete diseases

: Soilborne oomycete diseases, represented by Phytophthora and Pythium , pose a persistent challenge to the management of crops and perennial woody plants owing to the long-term survival and recurrent nature of these pathogens. Conventional target-site fungicides often exhibit inconsistent field efficacy and an elevated risk of resistance development under prolonged use. Fosetyl-aluminum (fosetyl-Al), a systemic fungicide that is rapidly converted to phosphite (Phi), displays a mode of action distinct from that of direct antimicrobial agents. Its disease control efficacy is achieved through two complementary mechanisms. At one level, it shows direct inhibitory activity against oomycetes by limiting spore germination, mycelial growth, and sporulation, in part via disruption of pathogen energy metabolism. More importantly, its primary mode of action involves the induction and amplification of host defense responses, including increased phytoalexin accumulation, enhanced expression of pathogenesis-related (PR) proteins, and strengthened cell wall architecture, ultimately conferring improved resistance to oomycete infection. Accumulating evidence further suggests that fosetyl-Al exerts minimal direct disturbance on soil microbial communities and exhibits good compatibility with arbuscular mycorrhizal fungi and diverse plant growth-promoting rhizobacteria, with its effects on the rhizosphere microecosystem occurring mainly through improvements in host physiological status. Within integrated pest management (IPM) frameworks, fosetyl-Al is therefore more appropriately positioned as a functional agent that supports host health and modulates disease progression, rather than as a rapid curative fungicide, acting synergistically with fast-acting chemicals, biological control agents, and agronomic practices. Based on current research consensus, this review further summarizes existing limitations, and outlines future research priorities and application strategies for fosetyl-aluminum in sustainable agricultural production and forest health management.