ABSTRACT
The seaweeds are a natural source of bio-fertilizer, plant growth regulators and bio-stimulants. The huge biomass of these marine macro-algae has the potential to become a renewable and economic source of input for sustainable agriculture. The extracts of marine macro-algae are extensively used as liquid fertilizers in crop production. The seaweed extracts are also rich in growth-promoting hormones like auxins, gibberellins, cytokinins, abscisic acid, ethylene, polyamines and quaternary ammonium molecules like betaine. The seaweed extracts are rich in micronutrients, vitamins, amino acids and antibiotics. The seaweed extracts can induce tolerance of crops to several abiotic stresses like drought, heat and cold. This may be attributed to the presence of the stress hormone abscisic acid and osmoprotectants like proline and glycine betaine in the algal extracts. The extracts of marine algae like Ascophyllum nodosum, Macrocycstis pyrifera, Ecklonia maxima, Durvillea Antarctica, Durvillea protatorum, Porphyra perforate, Fucus vesiculosus, Caulerpa paspaloides, Sargassum heterophyllum, Chara globularis, Sargassum muticum, Enteromorpha prolifera, Cyanidium caldarium, Laminaria digitata, Ulva lactuca, Nereocystis spp., Kappaphycus spp. and Gracilaria spp. have been used as liquid bio-fertilizers and biostimulants. The seaweed extracts as source of plant nutrients and plant growth regulators are discussed in this chapter.
