Utilization of Durvillaea antarctica (Chamisso) Hariot Extract as a Biostimulant to Enhance the Growth of Cucumber ( Cucumis sativus L.) Seedlings

Seaweed extracts are widely used as biostimulants in agriculture, with Ascophyllum nodosum (L.) Le Jolis, Ecklonia maxima (Osbeck) Papenfuss, and Macrocystis pyrifera (L.) C. Agardh representing the most commonly used seaweeds. In the present study, the suitability of the abundant and sustainable seaweed Durvillaea antarctica (Chamisso) Hariot as a raw material for biostimulant production was investigated. A thermo-acid method was used to prepare extracts of the brown algae D. antarctica extract (DAE) and A. nodosum extract (ANE) and compared by examining their growth promotion on cucumber seedlings. Germinated cucumber seedlings were grown in soil medium for 7 days and then treated with extracts for another 16 days until the third true leaf was fully extended, and the seedlings were harvested for analysis. The results showed that DAE treatment, at medium (0.12 g·L −1 ) and high (0.24 g·L −1 ) concentrations, improved growth parameters such as height and root length of cucumber seedlings. Biochemical analysis revealed that DAE increased the chlorophyll content and levels of indole-3-acetic acid, gibberellin, and nitrate reductase activity in cucumber seedlings, which could be partly responsible for the plant growth promotion effects. Plant height, chlorophyll content, and nitrate reductase activity of DAE-treated cucumber seedlings were significantly enhanced over those of the ANE treatment, suggesting the greater potential applications for D. antarctica in agricultural production when prepared using a thermo-acid extraction process.