Synergistic Impacts of ZnO-NPs and <i>Pseudomonas fluorescens</i> on Yield, Agronomic traits, and Physiological Factors to Enhance the Drought Resilience in Pakistani Rice Varieties

Among the abiotic stresses, drought is one of the main contributors to constraint rice productivity in arid and semi-arid areas in Pakistan. The present study aimed to evaluate the individual and combined impact of ZnO-NPs, Pseudomonas fluorescens (PGPR) on growth and biochemical attributes of drought-stressed rice. The experiment had a total of eight treatments like, untreated control, and application of ZnO-NPs alone, PGPR alone and their combination under both normal irrigated as well as drought conditions. Our study showed that drought stress control (DC) significantly decreased the morphological parameters including plant height, number of tillers, fresh biomass, number of panicles, 1000 grain weight and total grain yield as well as chlorophyll content, root length and dry root biomass compared to normal control (NC). In spite of using ZnO-NPs and PGPR individually and in combinations led to significant improve the drought stress effects. The plant height (115 cm), tiller numbers (24), fresh biomass (260 g), number of panicles (16.4), grain yield per plant (55 g.), chlorophyll content (40 SPAD value), root length (30.6 cm) and dry root biomass per plant (35 g) were improved with the combined treatment of drought conditions(Dcomb). In contrast, the highest values of most measured traits were consistently observed in Ncomb, which implied an individual or a combined effect between ZnO-NPs and PGPR. Increased performance of ZnONPs by promoting zinc nutrition, in tandem with conventional helper PGPRs such as phytohormone production and nutrient solubilization. This combination is possibly due to an increase in nanoparticle bioavailability facilitated through PGPR and microbial resilience under drought supported by ZnO-NPs. Among root traits, which are deeply involved in water or nutrient uptake and stress resistance in general, the most positive responses were attributed to root length and biomass under combined treatment. In conclusion, ZnO-NPs + Pseudomonas fluorescens co-application had promising effects in controlling drought stress and rice yield reduction under field condition through meaningful complementary physiological and biochemical mechanisms. The present study demonstrates an integrated nanotechnology and microbial approach for sustainable rice production under a rainfed ecosystem under climate change and water-limited conditions.