Control of Phytophthora melonis damping-off, induction of defense responses, and gene expression of cucumber treated with commercial extract from Ascophyllum nodosum

This study examined the effects of Marmarine, a marine plant extract formulation from Ascophyllum nodosum, on Phytophthora melonis. Greenhouse cucumber plants were sprayed and/or root drenched using Marmarine at 0.5 or 1 % concentration twice at 10-day intervals. Treatments also included application of fungicide (metalaxyl, 2 g L-1) alternating with Marmarine application. Treated plants were inoculated with P. melonis. Marmarine application resulted in a significant reduction in disease incidence of pathogen tested. Combined spray and root drenching with Marmarine was more effective than either spray or root drenching alone. The alternation of one fungicide application, alternated with Marmarine application, was highly effective and found to be the best treatment in reducing the disease ratings. Plants treated with Marmarine showed enhanced activities of various defense-related enzymes including beta-1,3-glucanase, peroxidase, and polyphenol oxidase. Altered transcript levels of various defense genes, including cucumber pathogen-induced 4, lipoxygenase, phenylalanine ammonia lyase, and galactinol synthase, were observed in treated plants. Cucumber plants treated with Marmarine also accumulated higher level of phenolics compared to water controls. These results suggest that seaweed extracts enhance disease resistance in cucumber probably through induction of defense enzymes and genes.