Auxin producing plant growth promoting bacteria enhance temperature stress tolerance in Chilean common bean landraces.

Current climate change challenges, including rising temperatures, reduced water availability, and increased soil salinity, pose severe threats to global agricultural productivity. While plant growth promoting bacteria (PGPB) have been studied for their role in stress mitigation, their application in enhancing heat tolerance in Chilean landraces of common bean (Phaseolus vulgaris L.) remains largely unexplored. This study evaluated the interaction between native PGPB and genetically distinct Chilean common bean landraces, which are part of the Andean gene pool and represent a socio-cultural food heritage. Auxin production and root adhesion capacity were first validated for two native Bacillus strains. Subsequently, their effects on heat-stressed plants were assessed at physiological and biochemical markers associated with thermal stress tolerance. Although PGPB inoculation improved certain stress-related responses at 30-35 °C in the Tórtola and Sapito landraces, growth responses at 40 °C in Mantequilla were observed even in control plants, indicating an inherent thermotolerance rather than a treatment-specific effect. Furthermore, although individual PGPB strains positively influenced traits such as root development and oxidative stress mitigation, the bacterial consortium did not show additive or synergistic effects under the tested conditions. These findings highlight the importance of host genotype and microbial compatibility in shaping plant responses under thermal stress. This study contributes novel insights into the role of PGPB in Chilean bean landraces and provides a foundation for future efforts in developing climate-resilient agroecosystems through targeted microbial applications.