Phytophthora infestans is a highly destructive oomycete for Solanum tuberosum (potato), causing late blight disease with significant yield losses worldwide. While resistance (R) genes and targeted editing of susceptibility (S) genes have been widely investigated for disease management, the functional dynamics of Sgenes during infection are less understood. In this study, we investigated cultivardependent differences in late blight susceptibility and the expression of Sgenes during different infection stages. Desiree was the most susceptible cultivar, followed by Lady Rosetta, Sante, Cardinal, Asterix, Coroda, and Mozika. While no visual tuber blight symptoms were observed, infected plants produced a significantly higher number of smallersized tubers, which suggests the impact of foliage late blight. Among the candidate Sgenes, expression analysis revealed that StDMR6, StPMR4, and StCESA3 underwent consistent early induction (5 dpi) across all susceptible cultivars. However, by 15 dpi, expression patterns became cultivarspecific; induction was sustained in Cardinal and Desiree but suppressed in Coroda and Lady Rosetta. The early induction of Sgene(s) at 5 dpi likely depicts facilitated pathogen colonization, while sustained expression at 15 dpi indicated a stable role during later stages of infection. Our findings highlight the critical involvement of Sgenes, particularly StPMR4, in mediating cultivarspecific susceptibility to P. infestans and provide potential targets for developing late blightresistant potato through genome editing.
Keywords: Phytophthora infestans, Solanum tuberosum (potato), Late Blight, Susceptibility Genes, Quantitative PCR
