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 attempted to refine the community structure by either adding or removing them based on their inhibition potential and plant-growth-promoting traits.

We used a plate-based method and plant assays to evaluate the biocontrol efficacy of S8, C7, and C8 against four major corn pathogens: Pythium torulosum, Fusarium graminearum, Fusarium subglutinans, and Rhizoctonia solani. We monitored the integration of strain S8 into the C7 community by measuring 16S abundance over 15 days post-incubation. Additionally, we conducted plant assays in pots under controlled conditions, focusing on the root-rot pathogen Pythium torulosum. We selected community members based on plant height, root biomass, supernatant assays, and auxin and siderophore production levels to create subcommunities that exhibited biocontrol activity and further stimulated plant growth.

Plate assays revealed that S8 and the modified consortium C8 showed greater inhibition of P. torulosum (>65% growth inhibition) than the original C7 community, 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 with C7 and C8. However, integrating S8 into C7 did not enhance overall biocontrol efficiency. Community analysis via 16S amplicon sequencing revealed no significant shifts in C7 community strain abundance following S8 introduction, suggesting that S8 failed to persist or maintain proportional representation within the community under in vitro conditions. Given that some individual strains exhibited biocontrol activity comparable to C7, while a few strains showed stronger pathogen suppression and had variable effects on root biomass and plant height, we designed three sub-communities (SC1, SC2, SC3) based on the highest inhibitory activity against the pathogen. Plant assays showed that inoculation with SC1 and SC2 not only restored but also enhanced plant height and root biomass.

These results indicate that biocontrol efficacy is primarily driven by specific strain combinations rather than by 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.