Comprehensive evaluation of biostimulants on leaf-level physiology, water use efficiency, and tuber quality in potato (

The pressing need for sustainable agriculture and food security has led to increased interest in biostimulants (BS) to mitigate abiotic stresses such as drought. This study provides a comprehensive evaluation of five commercial BS (Vesta, Humifirst, Acadian, SilicaPower, and Crop-Set) on leaf-level physiology, water use efficiency (WUE), tuber yield, and tuber quality in potato under drought stress. Drought stress was applied at the onset of tuber initiation (51 days after planting) and lasted for 7 days followed by a 4-day recovery period. Drought stress significantly decreased leaf relative water content, photosynthetic parameters, and flavonol index compared to non-drought. The yield and glucose content were 26% and 21% lower, and the sucrose content was 59% higher in the tubers of the drought-stressed plants than in non-drought-stressed. BS effects were generally limited and dependent on water conditions, with significant interactions observed for WUE parameters. Under drought conditions, Vesta and SilicaPower increased intrinsic WUE by 36% and 30%, respectively, while instantaneous WUE increased by 25% with both Vesta and Humifirst and by 33% with SilicaPower. Under non-drought conditions, Acadian led to a 42% increase in intrinsic WUE and a 60% increase in instantaneous WUE. However, these effects were not consistently accompanied by improvements in photosynthesis, biomass, or yield. Overall, this comprehensive assessment indicates that tested BS exert limited effects on potato plant biomass and tubers yield under drought stress, with their primary influence restricted to increased leaf-level WUE and changes in tuber composition rather than providing broad drought stress alleviation at whole plant level.