Integration of rhizobacterial mixture and silicon nutrition shows potential for the management of charcoal rot of sunflowers caused by Macrophomina phaseolinain semi-arid regions

Charcoal rot (CR), caused by Macrophomina phaseolina, is a major disease of sunflowers in semi-arid regions with poor soil conditions. There are fungicide-based strategies to mange this disease; however, alternative eco-friendly control approachs are needed to prevent further deterioration for the environment. This study describes CR control in sunflower grown in calcareous soil using a talc-based bioformulation containing a mixture of rhizobacterial strains (Azotobacter chroococcum, Azospirillum brasilense, and Klebsiella pneumoniae) integrated with silicon nutrition. The study was conducted under greenhouse conditions; M. phaseolinawas inoculated in the soil, and rhizobacterial strains were applied as seed treatment, as well as soil drenching at 7, 30, and 45 days after planting (DAP). As the silicon source (Si), potassium silicate was added to nutrient solution at a concentration of 2 mM and applied weekly starting from 7 DAP. The plants, collected at 85 DAP, showed that applying rhizobacteria and Si individually and in combination was effective in controlling CR disease and improving plant growth. The treatment that included rhizobacterial mixture and Si nutrition had a synergistic effect and resulted in the highest reduction (P< 0.05) in the disease incidence (65.3%), root-rot index (57.8%), and stem tissue colonization (63.6%) compared to non-treated inoculated control. Also, the decrease in the growth and nutrient uptake of sunflower plants due to the pathogen-induced stress was significantly reduced. Notably, rhizobacteria + Si treated-plants exhibited less lipid peroxidation and more phenolic and lignin contents with greater defence enzyme activities due to reduced root damage during M. phaseolinainfection. Therefore, the integration between rhizobacterial inoculation and Si fertilization can be a good candidate for managing CR in sunflowers in semi-arid regions.