Restoration of aged seed vigor and abiotic stress mitigation in tomato (Solanum lycopersicum L.) using microalgal biopriming

Abiotic stresses and declining seed vigor are primary constraints on tomato (Solanum lycopersicum L.) establishment. Microalgal protein-rich extracts are emerging as sustainable biostimulants. This study evaluated the efficacy of protein extracts from Chlorella vulgaris (CV) and Scenedesmus acutus (SA) as biopriming agents for new and aged (1-year) tomato seeds. Seeds were primed (8 h) in extracts at three concentrations (10%, 50%, and 100% relative to the stock) and evaluated in vitro stress assays (100 mM NaCl, 15% PEG-6000, and 45°C accelerated aging) and an in vivo seedling establishment trial under shade-mesh conditions. In vitro, CV-50 and CV-100 treatments significantly (p<0.05) improved the vigor index and seedling biomass under 100 mM NaCl stress compared to the untreated control. Critically, in vivo, SA-100 priming of aged seeds increased final emergence to 96%, a 15% (p<0.05) improvement over the 84% emergence of the aged control, resulting in emergence performance comparable to that of new seeds. This restoration was associated with significant (p<0.05) physiological enhancements in the established seedlings, including a 92% increase in Chlorophyll b content (1.24 mg g-¹ vs 0.65 mg g-¹ control) and a significant stimulation of root biomass. Microalgal protein-rich extracts, particularly SA-100. Overall, effective biopriming agents for improving the establishment of aged tomato seeds effective biopriming agents that can restore aged seed vigor by modulating root system architecture and enhancing photosynthetic efficiency during seedling growth establishment.