SEAWEED-DERIVED BIOSTIMULANTS: A SUSTAINABLE APPROACH FOR ENHANCING SEED GERMINATION AND EARLY ABIOTIC STRESS TOLERANCE

Abstract

Seaweed-derived biostimulants offer a sustainable approach in improving seed germination and the resilience of young plants to abiotic stresses. However, existing reviews have largely focused on foliar and field applications, leaving a fragmented evidence base for seed-stage applications that is rarely synthesised across physiological, biochemical and molecular scales. This review addresses this gap by critically synthesising research on the classification, biochemical composition, extraction methods and mechanisms of action of seaweed biostimulants, with a particular focus on seed-based applications. Brown, red and green seaweeds contain polysaccharides, phytohormones, phenolic compounds and osmoprotectants, though their relative abundance varies substantially with species, harvest season and extraction method. This batch-to-batch variability remains a major challenge limiting the reproducibility and commercialisation of seaweed biostimulants. Extraction techniques range from conventional aqueous, alkaline and enzymatic methods to emerging ultrasound-, microwave and supercritical fluid assisted approaches, with no single method providing the best balance between bioactive recovery, scalability, cost-effectiveness and environmental sustainability. At physiological, biochemical and molecular levels, seaweed extracts accelerate metabolic activation, reserve mobilisation, antioxidant defence and stress-responsive gene expression. This review presents an integrated mechanistic framework linking these responses. Cross-study comparison of seed-priming trials involving cereals, legumes and vegetables indicates consistent improvements in germination speed, uniformity and seedling vigour under salinity, drought and heat stress, though gaps persist in field-scale validation and long-term formulation stability. In conclusion, specific research priorities are identified such as standardised dose response protocols, omics based mechanistic validation and seed pelleting delivery systems as the most direct route from laboratory findings to climate resilient seed technologies.