Mitigating Combined Stresses Motivated by Salinity and Rhizoctonia solani using Brassinolide, and Azotobacter chrocoocum Enriched Biochar in Faba Bean (Vicia faba)

Faba bean (Vicia faba L.) is one of the major legume vegetable cultivated in Egypt. Naturally occurring biotic and abiotic stressors significantly reduce the growth and yields of crop plants. This study explored the potential of exogenous brassinolide (BL) application (10-7), biochar, Azotobacter chroococcum, and A. chroococcum enriched biochar to alleviate the negative impacts of the combined stresses of salinity and Rhizoctonia solani on faba beans. Brassinolide and Azotobacter sp. enriched biochar treatments were effective in mitigating the negative impacts of the combined stresses by reducing R. solani incidence by 28 and 20%, respectively, and disease severity up to 35 and 30%, respectively. The growth parameters include plant height, as well as the fresh and dry weight of both the roots and shoots were promoted. Total chlorophyll (TCC) and carotenoids contents (CC) of faba bean combined stress treated plants significantly increased after BL (18.1 and 22.9 mg g-1 FW, respectively) and Azotobacter sp. enriched biochar (13.4 and 17.9 mg g-1 FW, respectively) treatments. Peroxidase (POD), polyphenol oxidase (PPO) and ascorbate peroxidase (APX) enzymes activities were upregulated after Azotobacter sp. co-culturing and BL treatments. Meanwhile, superoxide dismutase (SOD) significantly decreased compared to treated controls. Additionally, Azotobacter sp. enriched biochar treatment highly significant increased SOD activity compared to controls groups. These results suggest that these compounds tested can contribute to more sustainable management practices for faba bean cultivation when exposed to saline stresses and R. solani infections.