Quantification of plant growth biostimulants, phloroglucinol and eckol, in four commercial seaweed liquid fertilizers and some by-products

Kelp species such as Ecklonia maxima are widely used as sources of liquid fertilizer for many economically important crops. Phloroglucinol and eckol are active biomolecules isolated from the brown seaweed Ecklonia maxima. They have shown root and growth promoting activity in some crop species. Currently there are many seaweed liquid products available in the markets that are sold as plant biostimulants. In some of these products auxins, cytokinins, polyamines, gibberellins, abscisic acid and brassinosteroids have been quantified and their role in plant growth and development has been well established. But, the presence and quantification of phloroglucinol and eckol in these products have not been determined yet. This would be useful for quality control of the products. In this study, four commercially available seaweed liquid fertilizers were analyzed for phloroglucinol and eckol content using High Performance Liquid Chromatography (HPLC). Additionally, a seaweed dry cake product ('Plant it' manufactured by Kelpak® from Ecklonia maxima) and Kelpak® cell wall paste by-product were also assessed for phloroglucinol and eckol content. The liquid seaweed products evaluated in this study were prepared from the seaweeds Ascophyllum nodosum, Durvillaea potatorum and Ecklonia maxima. HPLC analysis of these products showed that eckol content was greater than the known plant growth regulator phloroglucinol in three products. The amount of eckol detected in all the samples ranged from 96 to 860 μg L− 1. A higher quantity of both phloroglucinol and eckol was recorded for Kelpak® in comparison to the other products. The higher levels of these two plant growth promoting biomolecules in the Kelpak® samples can be attributed to the use of cold cellular-burst technology. More studies are necessary to determine the optimum levels of phloroglucinol and eckol required for plant growth in different liquid seaweed fertilizers.