Effect of mannitol from Laminaria japonica, other sugar alcohols, and marine alga polysaccharides on in vitro hyphal growth of Gigaspora margarita and root colonization of trifoliate orange.

摘要

A compound that stimulated the growth of an arbuscular mycorrhizal (AM) fungus was isolated from 75% methyl alcohol (MeOH) extracts of a brown alga, Laminaria japonica Areschoug, using high-pressure liquid chromatography (HPLC). This compound (Compound 1) was identified as mannitol by HPLC and nuclear magnetic resonance (NMR) spectroscopy. Compound 1 and purchased polysaccharides (alginic acid, fucoidan, carrageenan and mannan from marine algae) were tested for in vitro hyphal growth of an AM fungus, Gigaspora margarita Becker and Hall. Compound 1 (50-500 mg L-1) and carrageenan (1000 mg L-1) significantly stimulated the hyphal growth of germinating spores of Gi. margarita. The application of 100 mg L-1 of Compound 1 to trifoliate orange (Poncirus trifoliata Raf.) inoculated with Gi. margarita promoted root colonization and increased plant growth. These results suggest low concentrations of mannitol are among the reasons for enhanced hyphal growth and root colonization by the application of algal extracts. Other sugar alcohols (100-300 mg L-1 of xylitol, sorbitol and meso-erythritol) also increased the hyphal growth of Gi. margarita..