Refining the root-associated microbial consortia for enhanced biocontrol of the root-rot pathogen of corn

Microbial consortia play a crucial role in plant protection by suppressing soil-borne pathogens. A previously studied root-associated microbial consortium consisting of seven bacterial strains (C7) demonstrated biocontrol activity against seedling blight in corn caused by Fusarium verticillioides. To enhance its biocontrol potential, we incorporated a free-living bacterial strain (S8) exhibiting biocontrol activity, forming a modified community (C8). We evaluated the biocontrol efficacy of S8, C7, and C8 against four major corn pathogens: Pythium torulosum, Fusarium graminearum, Fusarium subglutinans, and Rhizoctonia solani. Plate assays revealed that S8 and C8 exhibited the highest inhibition against P. torulosum (>65% growth inhibition) but were less effective against Fusarium species (25-30%), while none of the communities restricted R. solani growth. In pot assays under growth chamber conditions S8 alone exhibited superior pathogen suppression compared to C7 and C8. However, integrating S8 into C7 did not enhance overall biocontrol efficacy. Community analysis via 16S amplicon sequencing revealed no significant shifts in C7 community strain abundance upon S8 introduction, suggesting a lack of establishment of S8 into the C7 community. Given that some individual strains exhibited stronger pathogen suppression than C7 and had variable effects on root biomass and plant height, we designed three sub-communities (SC1, SC2, SC3) based on the highest inhibitory activity. Plant assays demonstrated that inoculation with SC1 and SC2 restored plant height and root biomass, indicating that biocontrol efficacy is primarily driven by specific strain combinations rather than the broader community. Our findings underscore the importance of refining microbial consortia to maximize synergistic interactions and minimize antagonism, advancing sustainable disease management in agriculture.