Heat stress is a major abiotic constraint that reduces tomato productivity by disrupting plant physiological processes. It is hypothesised that thermotolerant bacteria within the plant microbiome can help sustain plant growth and physiological performance under high temperatures, thereby offering a novel strategy for plant growth promotion and heat stress alleviation. In the present study, 22 thermotolerant bacterial isolates associated with the heat-tolerant tomato genotype IIHR-2202 were isolated and evaluated for their plant growth-promoting traits at 30 °C and 42 °C under in vitro conditions. Ammonia production ranged from 12.86 to 34.10 µg mL-1 at 30 °C, while it ranged from 7.01 to 24.47 µg mL-1 at 42 °C. Phosphate solubilisation ranged from 41.86 to 88.83 µg mL-1 at 30 °C and from 13.40 to 61.95 µg mL-1 at 42 °C. Potassium solubilisation ranged from 31.45 to 63.92 µg mL-1 at 30 °C, whereas at 42 °C it ranged from 48.39 to 66.49 µg mL-1. Zinc solubilisation ranged from 32.70 to 48.95 µg mL-1 at 30 °C and 28.45 to 40.95 µg mL-1 at 42 °C. Siderophore production ranged from 32.11 to 47.36 PSU at 30 °C and 22.75 to 40.21 PSU at 42 °C. The isolates also retained significant indole-3-acetic acid (IAA) and gibberellic acid (GA₃) production under heat stress conditions. Based on their overall plant growth promotion traits six superior thermotolerant isolates were further identified by 16S rRNA gene sequencing as Fictibacillus phosphorivorans strain S3, Stenotrophomonas maltophilia strain S9, Glutamicibacter mishrai strain R6, Exiguobacterium indicum strain R7, Enterobacter soli strain R21 and Enterobacter hormaechei subsp. xiangfangensis strain S7. This is the first study evaluating multifunctional thermotolerant plant growth-promoting bacteria (PGPB) associated with the heat tolerant tomato genotype IIHR-2202 under in vitro elevated temperature. These thermotolerant PGPB are promising candidates for the development of microbial inoculants to improve tomato productivity under elevated temperature scenarios.
