Plant-Growth-Promoting Bioagents: A Sustainable Tool for Improving the Soil Health, Enhancing the Growth and Antioxidative Defense System of Tobacco

ABSTRACT: In the current era, the most crucial matter is to increase crop yields sustainably. Biological agents’ usage is an effective and environmentally friendly way to boost plant growth by activating the antioxidative defense system and improving soil health. The present investigation aimed at evaluating the bacterial (Bacillus subtilis, Bacillus amyloliquefaciens) and fungal (Trichoderma harzianum) bioagents in the sole and synergistic forms to improve tobacco (cultivar: Yunyan 87) growth by the mediation of antioxidant defense system and soil health. Bioagents were applied as root application at the rate of 100 ml suspension per plant after that same concentrations were applied 25 days of planting with four times taking 15 days intervals. Results revealed that soil application of these bioagents significantly enhanced growth, photosynthetic attributes, enzymatic antioxidants, and soil enzymatic activities. Combined application of bacterial and fungal bioagents improved the leaf area (121.50%), total chlorophyll contents (131.48%), polyphenol oxidase (PPO) (77.57%) and phenylalanine ammonia-lyase (PAL) activities (43.52%) as compared with control. Fungal bioagents marked better performance as compared to bacterial bioagents and control. The co-application of bioagents significantly enhanced the leaf quality attributes by decreasing the accumulation of proline, malondialdehyde content, and accumulation of chloride ions in tobacco leaves. The higher soil enzyme activities and essential nutrients were observed in the treatment of bacterial and fungal bioagents (application of Bacillus and Trichoderma spp.). In crux, the findings confirmed that the combined use of Bacillus and Trichoderma spp could contribute as a new cultivation practice for sustainable growth, productivity and quality of tobacco crop and can be recommended as safe and eco-friendly alternatives to preserve plant, soil, and human health for achieving the sustaibalility.