Microbial Biocontrol Agents and Natural Products Act as Salt Stress Mitigators in Lactuca sativa L.

One of the major problems related to climate change is the increase in land area affected by higher salt concentrations and desertification. Finding economically and environmentally friendly sustainable solutions that effectively mitigate salt stress damage to plants is of great importance. In our work, some natural products and microbial biocontrol agents were evaluated for their long-term effectiveness in reducing salt stress in lettuce (<i>Lactuca sativa</i> L. var. <i>romana</i>) plants. Fourteen different treatments applied to soil pots, with and without salt stress, were analyzed using biometric (leaf and root length and width), physiological (chlorophyll and proline content), and morphological (microscopic preparations) techniques and NGS to study the microbial communities in the soil of plants subjected to different treatments. Under our long-term experimental conditions (90 days), the results showed that salt stress negatively affected plant growth. The statistical analysis showed a high variability in the responses of the different biostimulant treatments. Notably, the biocontrol agents <i>Papiliotrema terrestris</i> (strain PT22AV), <i>Bacillus amyloliquefaciens</i> (strain B07), and <i>Rahnella aquatilis</i> (strain 36) can act as salt stress mitigators in <i>L. sativa</i>. These findings suggest that both microbial biocontrol agents and certain natural products hold promise for reducing the adverse effects of salt stress on plants.