The effect of oligosaccharides in an extract of the brown seaweed Ascophyllum nodosum on plant growth and plant immune responses in soybean (Glycine max L.) and duckweed (Lemna minor)

Abstract

Ascophyllum nodosum extract (ANE) is a processed brown seaweed extract used as a biostimulant. The known effects of ANE, when applied to plants in the aforementioned agricultural setting, include amplified plant growth, improved abiotic and biotic stress tolerance, enhanced fruit quality, and productivity. ANE contains partially hydrolyzed carbohydrates, proteins, hormones, and minerals from brown seaweed and its endophytic fungus, Mycosphaerella ascophylli. ANE is diluted down to a low concentration (e.g. 3mL/L or 0.3% ANE) and applied to a large area (1 to 2 L of ANE per acre). Thus, the bioactive component must be of a relatively high concentration in ANE. Carbohydrates are the major component of brown seaweed’s dry mass. During the ANE production process, insoluble carbohydrates are broken down into water-soluble oligosaccharides. Studies have shown that some oligosaccharides (e.g. oligoalginate and oligochitins) can increase plant growth and promote immune responses. Thus, the hypothesis of this study is that one or more of these oligosaccharide components (oligoalginate and/or oligochitin) in ANE is responsible for inducing improved plant growth and enhanced resistance to abiotic and biotic stresses. Soybeans and duckweed were used to test the hypothesis. No significant difference was found between the ANE treatment as a positive control and water treatment as a negative control in chlorophyll and phenolic content. Low light intensity and poor growth condition may be the limiting factors. Also, no significant difference was found between the water and ANE treatment in the number of duckweeds. Growth should be optimized for significant increase in population growth.