Cyanobacterial biostimulants boost tomato (Solanum lycopersicum L.) Growth and drought tolerance for climate-resilient cropping systems.

Since 2.4 Giga-annum, cyanobacteria have played a pivotal role in the oxygenation of Earth, supporting nitrogen availability through symbiosis with plants such as cycads, and enhancing growth, yield, and resilience to abiotic stresses, particularly drought induced by climate change. This research explores the effects of their lyophilized and aqueous extracts on tomato growth and stress resilience. The primary goal was to identify the cyanobacterial symbionts and evaluate the effects of the two biostimulant forms on tomato growth traits, in order to select the most effective for alleviating drought stress. The results indicated that the isolated strains belong to Desmonostoc sp., with the best performance observed in lyophilized biomass extracted from Desmonostoc sp. CH3C6 and C5. The experimental setup, involving single inoculations of the best performing strains and their co-inoculation revealed that inoculation enhanced root growth and relative water content, while negatively affected photosynthetic pigments. Inoculation with Desmonostoc sp. CH3C6 increased total soluble sugar (37.32 mg) and total phenol content (20.74 mg GAE (Gallic Acid Equivalent) /g), whereas proline (31.78 mg/g), catalase activity (0.002 U mg⁻¹ protein), and anthocyanin (0.101 mg/mL) biosynthesis were significantly improved by co-inoculation under stress. These findings reveal strain-specific responses to the derived biostimulant forms, with lyophilized biomass particularly improving tomato tolerance under water scarcity. Nevertheless, further research is required to understand crop specificity to biostimulant form, as well as the optimal application frequency and techniques.