Combined effects of paclobutrazol application and plant growth-promoting rhizobacteria (PGPRs) inoculation on physiological parameters of wheat (Triticum aestivum L.) under drought stress

Drought is a prominent abiotic stress that is exacerbated by climate change. The application of plant growth regulators (PGRs) and plant growth-promoting rhizobacteria (PGPR) has been considered an effective approach to mitigate adverse effects of drought stress. This study aimed to evaluate the effect of paclobutrazol (PBZ) and three rhizobacterial strains on various physiological parameters of wheat under drought stress. Experimental treatments consisted of three irrigation levels as the first main plot, and PBZ application at three levels as the second main plot. Furthermore, PGPR was applied at five levels as subplot. Results revealed that drought stress decreased relative water content (34%), chlorophyll fluorescence parameters, water use efficiency (WUE) (49%), Rubisco activity (40%), and increased antioxidant enzymes and malondialdehyde (52%), whereas PBZ treatment increased relative water content (RWC) (44%), and grain yield (WUEgy) (14%) compared to control treatment. Furthermore, the PGPR combination improved florescence parameters (by an average of 27%), catalase (34%), superoxide dismutase (22%), and nitrate reductase (34%) compared with control treatment. Moreover, grain yield correlated positively and significantly with chlorophyll content, and Rubisco and nitrate reductase activity, while it negatively correlated with malondialdehyde. In light of these findings, it is evident that a combination of PBZ and PGPR treatments emerges as a highly recommended approach for mitigating the adverse effects of water deficits, especially in the context of escalating climate change challenges.