Spatial dynamics of systemic acquired resistance-associated metabolites in the wheat cultivar fielder infected by Blumeria graminis f. sp. tritici

Introduction Systemic acquired resistance (SAR) is a whole-plant immune response in which localized pathogen attack primes distant tissues for enhanced defense. In Arabidopsis thaliana , this response is associated with the systemic accumulation of salicylic acid (SA), pipecolic acid (Pip), and N -hydroxypipecolic acid (NHP), but their spatial dynamics in wheat remain poorly understood. Methods Here, we investigated the spatial dynamics of SA, Pip, and NHP accumulation in the wheat cultivar Fielder following infection with the powdery mildew fungus Blumeria graminis f. sp. tritici . Their accumulation was examined between leaves, within a single leaf, and at 1–3 cm from the infection site. Results Infection induced strong local accumulation of all three metabolites, with NHP showing the largest response, increasing approximately 751-fold in infected primary leaves, 65-fold in the infected proximal leaf sectors, and 71-fold within infected lesions. Pip also increased markedly in infected tissues, whereas SA showed more moderate increases. These metabolic changes were accompanied by local induction of SA- and NHP-biosynthesis-related genes and pathogenesis-related ( PR ) genes. Despite the strong response at infection sites, protected distal leaves and non-infected tissues within the same leaf showed little or no accumulation of SA, Pip, or NHP. The same spatial restriction was observed for defense-related gene expression, while Bgt detection confirmed that fungal colonization was confined to infected regions. Discussion These findings indicate that Fielder develops a strong local defense-associated metabolic response to powdery mildew infection, but corresponding accumulation of SA, Pip, and NHP was not detected in non-infected tissues at the spatial scales examined. This spatial pattern differs from the systemic accumulation described in the Arabidopsis SAR model and suggests that systemic immune signaling in Fielder may not rely on long-distance accumulation of these metabolites.