Decoding Rhizosphere Synergies: Pseudomonas and Bacillus Enhance Microbiome-Mediated Suppression of Rhizoctonia solani in Sugar Beet

Sugar beet is a crucial sugar crop with substantial economic and nutritional value. The occurrence of damping-off disease severely impacts sugar beet quality and yield. Here, we successfully isolated two endophytes from sugar beet, and these were identified as Bacillus albus SB-3 and Pseudomonas chlororaphis SB-35 based on morphological observation and molecular identification. Both SB-3 and SB-35 exhibited nitrogen-fixing and potassium mobilization capabilities, with SB-35 demonstrating additional traits, including phosphate solubilization. SB-3 and SB-35 promoted the growth of sugar beet, resulting in increased biomass, and improved soil available nutrients. SB-3 and SB-35 had exhibited extracellular protease activities and inhibited the mycelium growth of Rhizoctonia solani. In independent pot experiments, SB-3 and SB-35 significantly controlled the damping-off of seedlings for sugar beet. Further analysis indicated that SB-3 and SB-35 may alter the microbial community structure, reducing the abundance of R. solani, promoting the recruitment of beneficial microorganisms, such as Hypocrea, Peziza, and Talaromyces, to occupy ecological niches, and thereby reducing pathogen load. The two bacterial strains modulated the diversity and community structure of rhizosphere microorganisms, suggesting a microbiome-mediated mechanism underlying their host-beneficial effects. This study advances our understanding of harnessing endophytes to enhance sugar beet productivity and suppressing sugar beet damping-off caused by R. solani.