Silk-trehalose seed coating technology preserves Rhizobium tropici viability and enhances zinc biofortification in common bean under marginal soil conditions

Sustainable food production requires global access to fertilizers, reducing yield gaps in marginal lands, and decarbonizing the agricultural sector. This study evaluates plant growth-promoting rhizobacteria (PGPRs) preserved in silk-trehalose seed coatings for six months under ambient conditions for their potential to enhance crop yields in challenging soils. Common bean seeds were coated with silk, trehalose, and Rhizobium tropici using a low-tech pan-coating method and tested in greenhouse experiments and field trials across three Moroccan experimental farms with contrasting soil types (favorable, low organic matter, and saline). Rhizosphere microbial communities were characterized using 16S rRNA gene sequencing, and grain nutritional quality was assessed by ICP-OES analysis. Coated seeds showed improved vigor, larger biomass, and enhanced root architecture compared to non-coated seeds under stress conditions. Field trials demonstrated that seed treatment was associated with 50-75% increases in yield parameters and a 53% increase in grain zinc concentration, depending on soil conditions. Additionally, the rhizosphere of treated plants exhibited an enhanced presence of beneficial microbes, such as Bacillus and Acidobacteria, without disrupting native bacterial communities. This low-tech seed coating approach offers a promising sustainable solution for enhancing food production and nutritional quality in resource-limited, environmentally challenged regions.