Abstract

This study investigates whether plant growth-promoting rhizobacteria (PGPR), melatonin (MEL), and strigolactone (STR), alone or in combination, counteract carbendazim (CAR) induced stress and restore pigment integrity, electron transport efficiency, and redox and osmotic equilibrium in chickpea seedlings. Certified chickpea seeds (Punjab Agricultural University, India), Pseudomonas putida strain (MTCC3315), and CAR (0.6 mM; inhibitory concentration (IC₅₀)). Surface-sterilized seeds were germinated for 10 days in Petri dishes (triplicate) under: Control, CAR, CAR + MEL, CAR + PGPR, CAR + MEL + PGPR, and CAR + MEL + PGPR + STR. PGPR was applied at 10⁹ cells mL^-1. Growth traits (fresh/dry mass, radicle/plumule), photosynthetic pigments, secondary metabolites, osmolytes and reactive oxygen species (ROS) were quantified by standard spectrophotometry; effects were evaluated. Absorbance-based assays and biomass measurements were recorded on 10-day seedlings, with results expressed per unit fresh/dry weight (FW/DW). CAR severely suppressed pigments and reduced carotenoids. PGPR partially restored pigments; MEL + PGPR improved stability; the triple consortium showed the most recovery and maximized carotenoids. Flavonoids rose ~3-fold with MEL + PGPR, while anthocyanins were highest with PGPR alone. CAR elevated trehalose, glycine betaine (GB) and proline; consortia generally reduced trehalose/GB toward control, with nuanced proline responses. PGPR lowered superoxide anion relative to CAR, whereas the consortium constrained hydrogen peroxide (H₂O₂), indicating balanced signaling and detoxification. Bio-priming with P. putida augmented by MEL and STR substantially alleviates CAR stress by restoring photosynthetic pigments, re-tuning osmolytes and moderating ROS, offering an eco-friendly adjunct to chemical disease management in chickpea.

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