Extracts from green and brown seaweeds protect tomato (Solanum lycopersicum) against the necrotrophic fungus Alternaria solani

Several reports have shown that crude or purified extracts of green, brown, and red seaweeds induce protection against fungal, bacterial, and viral pathogens in plants. In this work, we report that polysaccharide-enriched seaweed extracts obtained from green, Ulva lactuca and Caulerpa sertularioides, and brown algae, Padina gymnospora and Sargassum liebmannii, induced protection against the necrotrophic fungus Alternaria solani in tomato plants (Solanum lycopersicum). Protein activity of defense-related proteins polyphenol oxidase, guaiacol peroxidase and proteinase inhibitors together with expression levels of systemic wound response (SWRP) genes were also measured in leaf samples after algal extract treatment. All extracts were shown to reduce necrotic lesions induced by A. solani, particularly those obtained from U. lactuca and P. gymnospora. U. lactuca extracts induced the expression of SWRP genes, including defense, signal pathway, and protease genes, whereas those obtained from C. sertularioides, P. gymnospora and S. liebmannii showed almost no induction of SWRP genes, suggesting that extracts from the latter, whose carbohydrate composition varied from that of U. lactuca, may act through mechanisms other than the jasmonic acid/systemin wound-response pathway.