Agronomic evaluation of microalgal extracts as seed bio stimulants for improving germination and early growth of common bean

Microalgal extracts are rich sources of diverse bioactive primary and secondary metabolites with potential bio stimulatory effects. This study comparatively evaluated extracts from Chlorella vulgaris, Nannochloropsis salina, and Arthrospira platensis as natural seed-priming agents, aiming to identify the most effective species and optimal concentration for enhancing seed germination and early seedling development of common bean (Phaseolus vulgaris L.). Seeds were primed for 4 h in aerated algal extract solutions at concentrations of 0.0, 0.13, 0.25, 0.5, 1.0, 2.0, and 5.0%, followed by germination under controlled conditions (25-30 °C) for six days. Seed priming with algal extracts at concentrations up to 1.0% significantly improved germination percentage (GP), seedling vigor index (SVL), seedling length and biomass, and hydrolytic enzyme activities compared with untreated controls. The most pronounced stimulatory effects were observed at 0.5%, particularly with N. salina, which increased germination to 96% compared with 84% in the control, along with a ~ 130% increase in seedling vigor index. These enhancements were accompanied by elevated activities of hydrolytic enzymes and increased levels of total soluble sugars and proteins. Conversely, higher extract concentrations (2.0 and 5.0%) exerted inhibitory effects on germination and seedling growth, indicating a clear concentration-dependent response. Notably, S. platensis at 5.0% induced the largest decrease in GP (61%), along with a ~ 62.65% decrease in SVI.