Pectin-modified Nano-selenium inhibits Phytophthora capsici infection and enhances the nutritional quality of pepper fruits.

Phytophthora blight caused by Phytophthora capsici severely limits pepper production, and chemical fungicides induce pathogen resistance and reduce fruit quality. Nano‑selenium (nano-Se) shows biocontrol potential but suffers from poor stability. Here, metabolomic analyses were performed to explore the mechanism by which pectin-modified nano-Se (nano-Se@PT) acts in pepper. Results showed that nano-Se@PT enhanced plant resistance by modulating the phenylpropanoid pathway (elevating 6-nitrocoumarin by 30%) and the tricarboxylic acid cycle. Nano-Se@PT recruited beneficial rhizosphere microorganisms, particularly Lactobacillus and Bacteroides. For fruits, nano-Se@PT upregulated capsaicin biosynthesis (increasing capsaicin and dihydrocapsaicin by 27% and 103%, respectively) and elevated flavonoid and functional amino acid contents. These changes effectively suppressed lesion expansion on inoculated fruits (minimal lesion area after 5 days) and improved postharvest preservation potential. This study demonstrates nano-Se@PT as a promising biostimulant for integrated blight control, preservation, and nutritional enhancement in pepper.