Metabolomics in Biotic Stress: Insights into Potato Resistance to Powdery Scab

Powdery scab, caused by Spongospora subterranea, is a major disease of potato in which host resistance remains poorly understood at the biochemical level. While previous transcriptomic and proteomic studies have implicated glutathione S-transferases (GSTs) in cultivar-specific defence responses, orthogonal evidence at the metabolite level remains limited. In this study, untargeted metabolomics was applied to investigate root metabolic responses of two potato cultivars with contrasting resistance to S. subterranea. The relatively resistant cultivar 'Gladiator' and the susceptible cultivar 'Iwa' were inoculated with S. subterranea, and roots were collected at the stage of visible gall formation for analysis by high-resolution liquid chromatography-mass spectrometry (LC-MS/MS). Principal component analysis revealed a distinct metabolic profile in infected 'Gladiator' roots compared with both non-inoculated controls and infected 'Iwa' roots, indicating a stronger host metabolic response in the resistant cultivar. Among the annotated metabolites, cysteinyl-glycine (Cys-Gly), a central intermediate of glutathione turnover, was significantly more abundant in infected 'Gladiator' roots. The accumulation of Cys-Gly provides direct biochemical evidence linking enhanced glutathione cycling and GST activity to effective host defence. These findings highlight glutathione metabolism as a key component of potato resistance and demonstrate the value of metabolomics for additional validation of biochemical mechanisms underlying plant cultivar responses to biotic stress.