Activity of seaweed extracts and polysaccharide-enriched extracts from Ulva lactuca and Padina gymnospora as growth promoters of tomato and mung bean plants

Although marine seaweeds have been used as biostimulants since the beginning of modern agriculture, studies have only recently focused on the ability of seaweed extracts and their polysaccharides to enhance growth of plants. In this work, two bioassays were carried out to study the growth-promoting activity of seaweed extracts and polysaccharide-enriched extracts from Ulva lactuca and Padina gymnospora, obtained in neutral and alkaline conditions. Initially, the effect of seaweed extracts and polysaccharide-enriched extracts on seed germination and growth-promoting activity on tomato (Solanum lycopersicum cv. Rio Grande) plants under in vitro conditions was studied. Half-strength Murashige-Skoog (MS) medium with or without sucrose was supplemented with different concentrations of seaweed extracts (2, 4, and 10 mg mL(-1)) or polysaccharide-enriched extracts (0.2, 0.4, and 1.0 mg mL(-1)). The parameters evaluated were germination percentage, radicle and shoot length, and dry weight. In a second experiment, polysaccharide-enriched extracts at 1.0 mg mL(-1) and indole-3-butyric acid as the control were studied for root inducer activity in mung bean (Vigna radiata). The majority of seaweed extracts had an inhibitory effect on seed germination. However, a significant effect (P <= 0.05) on tomato seedling growth (except for dry weight) was shown with seaweed extracts at 2 mg mL(-1) included in half-strength MS medium with sucrose (30 g L-1). Moreover, 10 mg mL(-1) neutral and alkaline seaweed extracts had an inhibitory effect on the parameters evaluated. In contrast, polysaccharide-enriched extracts obtained from U. lactuca and P. gymnospora promoted germination and stimulated growth of tomato plants compared to the controls. Additionally, treatment of mung bean hypocotyl cuttings with polysaccharide-enriched extracts of U. lactuca and P. gymnospora induced rooting more rapidly and in greater number compared to the controls. These results provide evidence that polysaccharide-enriched extracts act as an effective growth-promoting treatment.