Alleviation of penthiopyrad phytotoxicity in cucumber via mesoporous nano-selenium: Insights into root exudate changes and improved photosynthesis

Penthiopyrad (PEN), a succinate dehydrogenase inhibitor (SDHI) fungicide, is widely used in agriculture; however, its misuse can induce phytotoxicity in cucumber. In our previous study, a dual-functional nano-pesticide (HPC@PEN@MSe) with both detoxification and growth-promoting properties was developed based on mesoporous nano-selenium (MSe) and hydroxypropyl cellulose (HPC). The present study investigated the regulatory effects of this nano-pesticide on cucumber root exudates and photosynthetic parameters under controlled hydroponic conditions. Cucumber plants were exposed to PEN (10 mg/L) or HPC@PEN@MSe (at an equivalent PEN concentration) for 14 days, with three biological replicates per treatment. Changes in cucumber root exudates under PEN and HPC@PEN@MSe stress were analyzed using ion exchange chromatography (IEC), synchronous fluorescence spectroscopy, three-dimensional (3D) fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and two-dimensional correlation spectroscopy (2D-COS). The results demonstrated that, compared with PEN treatment alone, HPC@PEN@MSe better preserved the chemical profile of root exudates, including amino acid composition, fluorescent components, and functional group characteristics. In parallel, leaf photosynthetic parameters were measured. After 14 days of exposure, the net photosynthetic rate in the HPC@PEN@MSe group was 2.17 times higher than that in the PEN-only group. In summary, these findings suggest that, in addition to its direct physiological protective effects, HPC@PEN@MSe may indirectly promote plant health by maintaining the overall stability of the root exudate chemical profile. This provides new insight into the rhizosphere ecological effects of functionalized nano-pesticides.