Effect of seaweed extracts on hyphal growth of vesicular-arbuscular mycorrhizal fungi and their infectivity on trifoliate orange roots

The effect of seaweed extracts on the hyphal growth of a vesicular- arbuscu lar mycorrhizal (VAM) fungus, Gigaspora ramisporophora Spain, and its devel opment on trifoliate orange roots was investigated. The seaweeds, Konbu (La minaria japonica Areschoug) and Wakame (Undaria pinnatifida Suringar), were extracted with 75% methanol (MeOH); these crude extracts were fractionated by a flash chromatograph equipped with a Chromatorex ODS DM1020T column (2 0x250mm) and eluted with 0, 10, 25, 50 and 100% MeOH. Both crude extracts had no effect on hyphal growth of VAM fungi. However, t he 25 and 50% MeOH eluates of Konbu (0.1 and 0.3gDW), and the 10 and 25% Me OH eluates of Wakame (0.1 and 0.3gDW) stimulated the growth of VAM hyphae. The most effective hyphal growth stimulation was in the 25% MeOH eluates of Konbu (0.3gDW). Crude extracts of Wakame (1.0gDW) and Konbu (0.2 and 1.0gDW) increased the percentage of VAM infection of trifoliate orange roots, compared with the c ontrol. The 25% MeOH eluates of Konbu (1.0gDW) and Wakame (1.0gDW) signific antly stimulated the percentage of VAM infection as compared with the crude extracts. The crude extracts and 25% MeOH eluates from both seaweeds had n o significant effect on the growth of trifoliate orange seedlings, compared with the control. The results suggest that the extracts, particularly the 25% MeOH eluates ob tained from both seaweeds, contain growth stimulatory substances for VAM fu ngi, and that the eluates applied to the soil stimulate VAM development in trifoliate orange roots.