Harnessing SynComs for rhizosphere engineering to alleviate salt stress in Vigna radiata: From lab experiments to the field.

Abiotic stresses such as salinity severely hamper plant productivity and threaten global food security. Rhizosphere engineering is an eco-friendly approach, which offers a sustainable strategy to improve plant and soil health, by manipulating root-associated microbial communities. In this study, synthetic microbial communities (SynComs) were assembled using bacterial strains previously isolated from the rhizosphere of Vigna radiata that had been acclimatized to salinity stress over multiple passaging cycles, by adopting a top-down approach of rhizosphere engineering. The bacterial strains isolated from the stress-acclimatized rhizosphere microbiome of Vigna radiata were screened for key plant growth promoting (PGP) traits, and ten top-performing isolates were selected to constitute 33 SynComs, with varying complexities. The SynComs were evaluated in controlled environments (growth chamber and nursery) and under field conditions for their ability to enhance plant growth and mitigate salt stress. Several SynComs significantly improved plant height, dry weight, and yield. Notably, application of SynComs 3, 10, 22, and 23 resulted in significant yield enhancement of plants, while SynComs 26-28 increased dry biomass by 34 % and led to a reduction in proline and malondialdehyde (MDA) levels by 22 % and 18 %, respectively, under field conditions. Amplicon sequencing of the 16S rRNA gene from soil samples revealed SynCom driven shifts in rhizosphere bacterial communities, supporting the observed physiological benefits in the field-grown plants. These findings demonstrate the potential of SynComs as efficient and scalable alternatives to native microbiomes for promoting plant stress resilience. Owing to their defined composition, and logistical ease of application, SynComs have emerged as promising tools for advancing sustainable agriculture in stress-prone environments.