Low-Dose Sargassum Spp. Extract as A Physiological Biostimulant For Lowland Green Curly Lettuce (Lactuca sativa L. Var. Grand Rapids)

Abstract

Green curly lettuce (Lactuca sativa L.) is a short-cycle leafy vegetable with high commercial potential; however, its expansion in lowland areas is constrained by reduced physiological performance during vegetative growth. Seaweed-derived biostimulants provide a sustainable approach because brown macroalgae such as Sargassum spp. contain phytohormone-like compounds, amino acids, minerals, polysaccharides, and phenolic compounds that may regulate growth and stress adaptation. This study evaluated the dose-dependent effect of Sargassum spp. extract on the growth and physiological response of Grand Rapids lettuce cultivated under lowland conditions. The experiment was conducted for two months at the MBKM Field and Agronomy Laboratory of INSTIPER Yogyakarta using a completely randomized design with four extract concentrations: 0, 5, 10, and 20 g L^-1, with three replications. The biostimulant was applied once through foliar spraying and root drenching. Observed variables included plant height, leaf number, leaf width, leaf greenness score, canopy diameter, nitrate reductase activity, soil NPK status, and photosynthetic-related parameters. The 5 g L^-1 concentration produced the strongest vegetative response, with plant height, leaf number, canopy diameter, and leaf width reaching 19.43 cm, 5.98 leaves, 19.71 cm, and 6.87 cm, respectively. In contrast, 20 g L^-1 reduced all growth variables below the control, indicating a concentration-dependent inhibitory effect. Therefore, 5 g L^-1 Sargassum spp. extract can be proposed as an initial effective dose for improving lowland lettuce growth, while higher concentrations require careful evaluation before field application.

Keywords: biostimulant, grand rapids lettuce, lowland cultivation, physiological response, Sargassum spp.