The influence of Ecklonia maxima seaweed extract on growth, photosynthetic activity and mineral composition of Brassica rapa L. subsp sylvestris under nutrient stress conditions

Over the past twenty years, several technological innovations have been proposed in order to enhance the sustainability of agricultural production systems through a significant reduction of chemicals. Plant biostimulants, like seaweed extracts (SWE) represent interesting tools for reducing the use of chemicals and improving crop tolerance to abiotic stresses, such as nutrient deficiency. The aim of the study was to determine growth, yield, photosynthetic rate, SPAD index, mineral composition and leaf quality of a greenhouse grown Brassica rapa L. subsp. sylvestris L. Janch. var. esculenta Hort., also known as friariello campano either untreated or treated (via root application) with Ecklonia maxima SWE. For root application, 100 mL of solution containing 3 mL L-1 of SWE were applied to the growing medium at weekly interval. Friariello campano ecotype plants were supplied with three nutrient solution concentrations: full strength (EC = 2.0 dS m(-1)), half strength (1.0 dS m(-1)) and tap water (0.5 dS m(-1)). Agronomical and physiological parameters were substantially reduced when the EC was 0.5 dS m(-1). Decreasing the EC in the nutrient solution from 2.0 to 0.5 dS m(-1) increased the hydrophilic antioxidant activity and total phenols contents. The half-strength nutrient solution should be adopted under our conditions due to similar crop performance to the full strength solution, and the higher leaf antioxidant activity and total phenolics, whereas the total ascorbic acid was reduced. Root application of SWE increased fresh and dry yield by 13.5% and 16.6%, respectively, as well as hydrophilic antioxidant activity in comparison to untreated plants. The better crop performance of friariello campano ecotype plants treated with SWE was associated with an improvement of their nutritional status (higher P and K and lower Na concentrations), higher photosynthetic rate and chlorophyll content in plants independently of nutrient concentration treatment. The positive effect of SWE application could be attributed to the composition of brown seaweed extracts, especially the presence of polysaccharides and osmoprotectants as betaines and betaine-like compounds.