Tomato seed priming with water-soluble polysaccharides from Jania adhaerens for the control of soil-borne pathogens

In Europe, controlling soil-borne pathogens is difficult as synthetic products for soil treatment have been restricted. Therefore eco-friendly alternative solutions are encouraged by international rules. Marine algae are a source of several bioactive compounds with applications in many sectors. Among these compounds, polysaccharides are well-known elicitors of plant defence responses to microorganisms and viruses, and abiotic stresses. However, more knowledge is needed on their activity against soil-borne pathogens through seed application. Water-soluble polysaccharides (WSPs) used in this study were extracted from the red alga Jania adhaerens by the autoclave-assisted procedure. They were first characterized by FT-IR spectroscopy and then applied at different concentrations (0.3, 0.6 and 1.2 mg/mL) to tomato seeds for testing their activity against the soilborne pathogens Fusarium oxysporum, Pythium ultimum and Rhizoctonia solani and for the elicitation of plant defence responses under greenhouse conditions. Our results showed that WSPs seed treatment in presence of the pathogens increased seedling emergence and plant development and reduced disease severity depending on the dose. The treatment without pathogen challenges differentially induced the expression of genes related to phenylpropanoid, chlorogenic acid, SAR and ISR pathways, and chitinase and β-1,3 glucanase activities, which may explain the pathogen control. In conclusion, WSPs from J. adhaerens are promising bioactive compounds for the control of soil-borne pathogens to be used in sustainable agriculture.