Salicylic Acid Plays a Major Role in Potato Defense Against Powdery Scab Pathogen, Spongospora subterranea f. sp. subterranea.

Potato powdery scab, caused by the soil-borne pathogen Spongospora subterranea f. sp. subterranea (Sss), poses a significant threat to potato production, reducing potato value and impacting fresh market quality. Effective management strategies for this disease are currently lacking, and Sss is widespread in many potato-growing regions, highlighting the urgent need for effective control measures. Although the use of disease-resistant cultivars holds potential as a sustainable solution, the genetic mechanisms underlying resistance to Sss remain unclear. In this study, we investigated the role of the defense-related phytohormone salicylic acid (SA) in potato resistance to Sss. Initial analyses of defense gene expression revealed transcriptional reprogramming in response to Sss infection in potato hairy root cultures. Quantification of defense-related phytohormones further demonstrated a significant increase in SA levels in Sss-infected roots, while other phytohormones, jasmonic acid and ethylene, showed no substantial variation. Pretreatment of hairy roots with SA resulted in a marked reduction in Sss propagation, suggesting that SA contributes to induced resistance against the pathogen. To further elucidate the role of SA, we utilized transgenic hairy roots overexpressing the SA receptor SlNPR1 to enhance SA sensitivity and expressing the bacterial nahG gene to degrade endogenous SA. Our findings showed reduced Sss growth in SlNPR1 overexpression lines, whereas nahG lines exhibited increased pathogen proliferation. These findings were further validated in fully grown potato plants using a pot assay. Collectively, our results indicate that SA plays a pivotal role in mediating resistance to powdery scab in potato.