Effect of Plant Growth Promoting Rhizobacteria and Biochar on Psysiology of Brassica napus L. under Induced Drought Stress

Abstract

Changing climate has caused severe water deficit stress that has become a serious environmental problem. In the age since the industrial revolution, production of greenhouse gases from fossil fuel combustion and deforestation have directed to global warming and climate change leading stress condition. Climate change induces biotic and abiotic stress conditions which badly disturb the yield of crops with leading to the biochemical and physiological damages to plants. Biochar and plant growth promoting rhizobacteria (PGPRs) alleviate the effect of drought condition consequently a field study was conducted to observe the inoculation and co-inoculation of Pseudomonas sp. and Staphylococcus sp. with biochar of Morus alba L. wood to alleviate the adverse effects of drought stress in two genotypes of Brassica napus L. including Punjab sarson and westar. Morphological structure and elemental analysis of biochar were obtained through scanning electron microscope (SEM) which revealed porous nature of biochar and energy dispersive X-ray spectroscopy (EDX) which showed Sodium, Megnesium, Calcium and Carbon elemental analysis. Physioco-chemical analysis of biochar showed 5.4 cmol kg-1 cation exchange capacity, 6.9 ds/m electrical conductivity, pH of 9.6, 0.50 g cm-3 bulk density, and organic carbon 3.64%. In the results biochar and PGPRs triggered an addition in physico-chemical properties of soil including water use efficiency (WUE), relative water content (RWC), percent moisture content (%MC), soil nutrients, percent field capacity (%FC) along with germination parameters including Timson germination index (TGI), final emergence percentage (FEP), mean germination time (MGT), final germination percentage (FGP), germination energy (GE), mean emergence time (MET), germination rate index (GRI) and emergence energy (EE). Vegetative parameters including seed vigor indexes, plant height stress index (PHSI), root to shoot ratio (RSR), leaf area ratio (LAR) and leaf area index (LAI) improved with the application of PGPRs and biochar as a carbon source. Significantly enhanced plant biomass, leaf area, plant height and root growth approved the effectiveness of this approach. Synergistic application of PGPRs and biochar significantly enhanced the photosynthetic chlorophyll pigments, carotenoid and anthocyanin content at p<0.05 level. SEM study revealed that biochar and PGPRs improved epidermal vigor and stomatal physiology. Malondialdehyde (MDA) and hydrogen peroxidase (H2O2) increased in drought stress which were then decreased by the application of biochar and PGPRs. Osmolytes content containing sugar, proline and glycine betaine (GB) were significantly enhanced at p<0.05 level under induced drought which were markably provoked by these growth regulators. Total flavonoids, phenolics and protein content along with antioxidant enzymes including peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were significantly suppressed at p<0.05 level under induced drought stress which were enhanced with inoculation of PGPRs and biochar. We concluded, that the co-application of PGPRs and biochar especially Staphylococcus sp. individually and in combination with biochar can be an effective approach to bridge the drought adversities in plants and to overcome yield restrictions in water deficit agro-ecosystems.