Panicum virgatum L. salt tolerance improved by inoculation with multi-stress tolerant Bacillus

Soil salinity is a key limiting factor for agricultural production, even for moderately salt-tolerant crops such as switchgrass (Panicum virgatum L.). We hypothesized that switchgrass resistance to salt stress will increase when seeds are inoculated with bacteria that support plant physiological (antioxidant enzymes, proline) and morphological (root system architecture) adaptations in salt-affected soil. In this study, we inoculated switchgrass seed with multi-stress tolerant bacteria, either Bacillus velezensis H1B18 or Bacillus mojavensis H1B5, and grew the seed in salt-affected soils with electrical conductivity from 0.5 to 9.8 dS m⁻¹. Compared to uninoculated switchgrass, plants inoculated with Bacillus strains had greater superoxide dismutase and catalase enzyme activities, which counteract oxidative stress, and accumulated 22-271% more proline after 4 wk. Furthermore, switchgrass inoculated with Bacillus maintained its root system architecture (root total length, surface area, and volume) as the soil salinity increased. This produced taller plants with more above-ground biomass. For example, the B. velezensis H1B18-inoculated switchgrass was 54-161% taller and had 3.3-7.4 times more shoot biomass than the uninoculated switchgrass. Overall, switchgrass resistance to salt stress was improved by multi-stress tolerant Bacillus that promoted plant growth, physiological and morphological traits in salt-affected soils.

The online version contains supplementary material available at https://doi.org/10.1007/s10725-026-01530-8.