Elucidating the phytotoxicity threshold of PGPR, ZnO/MnO-NCs and corncob biochar on physical and biochemical attributes of wheat under Cd stress.

Globally agricultural sector, like cereals and especially wheat, are facing a broad range of challenges like as biotic and abiotic stresses. The main purpose of this study was to check the phytotoxic thresholds of PGPR strain, zinc manganese oxide nanocomposites (ZnO/MnO-NCs), and corncob biochar on wheat (Triticum aestivum L.) under 20 mg L^-1 cadmium (Cd) stress. The ZnO/MnO-NCs were synthesized from leaf extract of Conocarpus erectus L. and characterized by using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR). The phytotoxicity threshold of the biosynthesized ZnO/MnO-NCs, PGPR, and corncob biochar were optimized. Various dosages (0, 50, 100, 150, and 200 mg L^-1) of the nanocomposites, biochar (0, 1, 2, 3, and 4%), and different PGPR strains (1, 2, 3, 4) were applied through soil drenching in 3 replicates. After six weeks plants were harvested, and marpho-pysio-biochemical parameters were measured. Results showed that optimal growth was achieved with 150 mg L^-1 of nanocomposites, 3% w/w biochar, and PGPR strain Bacillus Flexa. Overall, all the bio stimulants enhance morpho-physio-biochemical parameters in plants and reduce Cd toxicity. However, among the bio-stimulants tested, Bacillus Flexa sp. of PGPR was most effective in lowering Cd accumulation in the roots and shoots, showing a 15.35% and 17.71% increase in root length and 5.28% and 7.02% increase in shoot length compared to nanocomposites and biochar, respectively in the presence of cd stress. It also enhanced chlorophyll content and antioxidant enzyme activities while reducing oxidative stress markers. The soil-drenching application of these bio-stimulants has the efficiency to improve wheat growth, crop yield and reduction in uptake of Cd stress. Applying these bio-stimulants at optimized doses in contaminated soils can offer a sustainable, eco-friendly approach for improving crop yields while reducing cadmium accumulation in food crops.

Supplementary information: The online version contains supplementary material available at 10.1007/s12298-025-01625-y.