Unveiling the potency of rice field cyanobacterial strains for plant growth promotion and root colonization by deciphering the molecular elicitors

Soil cyanobacteria collected from paddy fields across six diverse locations were evaluated for their plant growth-promoting potential, specifically through cyanobacterial extracellular products (CEP) influencing Pisum sativum L. germination and subsequent morphometric traits. Out of 20 tested strains, Anabaena sp. MBDU 902 demonstrated radicle and plumule lengths of 4.59 cm and 1.75 cm, respectively, while Nostoc microscopicum MBDU 102 exhibited enhanced radicle and plumule growth responses of 60 % and 80 %. Strain prioritization was achieved through Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GAIA), where Nostoc commune MBDU 101 emerged as the most potent strain based on aggregate growth metrics. The bioactive extract of Nostoc commune MBDU 101 was purified and analyzed using Preparative High-Performance Liquid Chromatography (P-HPLC) and Liquid Chromatography-Mass Spectrometry (LC-MS), identifying key phytohormones, including Indole-3-butyric acid (IBA), Gibberellic acid, IAA conjugates, and long chain fatty acids, confirmed via agar slant bioassay. To elucidate its root association capabilities, hydroponic cultivation of Zea mays L. was conducted using Nostoc commune MBDU 101 culture and CEP, resulting in significant enhancement of seedling length, biomass, leaf dimensions, and lateral root development compared to control. Root colonization was validated through confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Gas Chromatography-Mass Spectrometry (GC–MS) revealed signaling molecules in culture filtrates essential for root association, underscoring Nostoc commune MBDU 101 robust plant growth-promoting attributes.