Discrete Roles for Extracts of Ascophyllum nodosum in Enhancing Plant Growth and Tolerance to Abiotic and Biotic Stresses

Elucidation of the precise roles of seaweed extracts in agriculture has been restricted by a widespread 'one-size-fits-all' approach to extraction, development and functional validation. In this study, we classify extracts of seaweed on the basis of their extraction, biochemical and functional properties therein and demonstrate discrete roles for high and low temperature-derived extracts of Ascophyllum nodosum in enhancing plant growth and tolerance to abiotic and biotic stresses. In brief, the biochemical properties of extracts were characterised and their potential influence on plant growth and health was investigated. Higher antioxidant levels were observed for a high temperature (HT)-derived extract (Super Fifty (R)) compared with a low-temperature (LT)-derived extract (Ecolicitor (R)), with a 32-fold difference detected (FRAP assay), therefore suggesting benefits conferred by HT-derived extracts in abiotic stress situations. Analysis of growth in saline and non-saline conditions gave contrasting results. In non-saline conditions, no significant difference between treatments was observed. However, in conditions of high salinity, a 42.5% increase in lettuce weight on treatment with HT-derived extract was observed compared to 28.5% with (LT)-derived extract. In contrast, the effects of biotic stresses were reduced more by LT-derived extract than by HT-derived extract, with local and systemic reductions in Sclerotinia sclerotiorum and Alternaria brassicae lesion diameters achieved on treatment with LT-derived extract. In conclusion, this study demonstrates a significant level of specificity linked to extraction type and supports a 'fitness-for-purpose' approach to validation of seaweed extract properties and their specific applications in agriculture.