Decoding Rhizosphere Synergies: <i>Pseudomonas</i> and <i>Bacillus</i> Enhance Microbiome-Mediated Suppression of <i>Rhizoctonia solani</i> 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 <i>Bacillus albus</i> SB-3 and <i>Pseudomonas chlororaphis</i> 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 <i>Rhizoctonia solani</i>. 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 <i>R. solani</i>, promoting the recruitment of beneficial microorganisms, such as <i>Hypocrea</i>, <i>Peziza</i>, and <i>Talaromyces</i>, 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 <i>R. solani.</i>