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Greenhouse-grown carrot plants were sprayed with an extract (0.2%) of the seaweed Ascophyllum nodosum (SW) and then inoculated 6 h later with the fungal pathogens Alternaria radicina and Botrytis cinerea. Additional applications of SW were made 10 and 20 d after inoculation. Treated plants showed significantly reduced disease severity at 10 and 25 d after inoculation compared to control plants sprayed with water. SW was more effective than salicylic acid (SA) (100 mM) in reducing infection. Activity of certain defence-related enzymes, including peroxidase (PO), polyphenoloxidase, phenylalanine ammonia lyase, chitinase and b-1,3-glucanase, were significantly increased in plants treated with SW and SA compared to the control 12 h after treatment. The treated plants also had higher transcript levels of pathogenesis-related protein I (PR-1), chitinase, lipid transfer protein (Ltp), phenylalanine ammonia lyase (Pal), chalcone synthase, non-expressing pathogenesis-related protein (NPR-1) and pathogenesis-related protein 5 (PR-5) genes compared to control plants. These results show that SW enhances disease resistance in carrot, likely through induction of defence genes or proteins.

Marine macroalgae or seaweeds are the major components of the marine flora and are used as food, feed and fertilizer. Applications of seaweed extracts (SEs) from certain algae have the potential to improve plant growth and yield. The richness of polysaccharides, oligosaccharides, peptides, proteins and phytohormones in various SEs, favor the deployment of SEs as bio-elicitors for disease tolerance in plants. The SEs from some algae regulate the physiological, biochemical and molecular mechanisms of the plants to enhance defence against pathogens. The SEs also modulate the rhizosphere microbial composition, which contributes to regulation of plant defence responses. The regulation of salicylic acid (SA) and jasmonic acid (JA)-signaling pathways, reactive oxygen species (ROS) homeostasis and defence-related genes/enzymes by applications of SEs play a major role in the molecular regulation of defence response. This review focuses on the bioactive molecules of various SEs, functional mechanism of bio-elicitors, phytohormones, and molecular regulation towards disease tolerance in plants.

It’s a move towards a more sustainable and responsible agriculture: growing marine algae (seaweed) would require no pesticides, hormones, and are virtually drought- resistant. And researchers have found that some types of algae grown in a cultured environment often produce a higher biomass of algae per cubic area than land-based crops like wheat and corn. The leafy sea crop is a low-calorie, low-fat source of protein and iron, and is full of nutrients like vitamin K, folic acid and calcium.

Norway, world-leading producer of farmed Atlantic salmon, is already on the map for utilizing natural stocks of algae and kelp in its cold, clean northern waters.

Since the beginning of salmon farming in the 1970s, Norway has been working hard to advance techniques in aquaculture and mariculture based on sustainable and ecologically safe growth and harvest practices. They have one of the most successful salmon farming operations worldwide, accounting for 54 percent of all farmed Atlantic salmon in 2016. Not surprisingly, the country is a source of innovation in techniques that the rest of the world have long valued for their own fish farming operations.

Research in seaweed has increased in line with a push for Scandinavian countries to take the lead in a Blue Bioeconomy — businesses based on the sustainable and smart use of renewable aquatic natural resources.

Seaweed aquaculture started here about 10 years ago, and already one can find over 20 companies in Norway involved in some way with seaweed cultivation.

Can one make seaweed aquaculture energy-efficient and eco-friendly?

In Chwaka Bay, aquaculture (the farming of aquatic organisms) is represented by a small-scale but much debated activity; farming of marine macroalgae, or seaweed farming. Aquaculture as a whole dates back several millennia in areas like South-East Asia, but has during the last decades become heavily promoted as an alternative livelihood in developing countries to (i) reduce pressure on overharvested natural resources (e.g. fish stocks) and (ii) supply cheap food and income (Tacon 2001). Many promises of this “Blue Revolution” have, however, not been fulfilled, because technical know-how and experience is often lacking (Dadzie 1992; Machena and Moehl 2001), and because some of the hitherto dominating forms (for example farming of giant shrimp/prawns) have been riddled with huge sustainability problems of their own (Deb 1998; Bryceson 2002).

Seaweed farming is, in comparison to e.g. intensive shrimp farming, an alternative form of aquaculture, which has been described as “the most sustainable” form of aquaculture. This is primarily because (i) farming can be conducted in shallow coastal areas or the open ocean (instead of in dugout ponds), (ii) the seaweeds require no addition of fertilizers or pesticides, only enough light and water mo- tion, (iii) the rapid growth rate (up to 15 percent per day) results in relatively short farming cycles (Mshigeni 1976; FAO 2002), and (iv) farming generates a cash income to farmers. Most open-water seaweed farming involves two genera of tropical red algae (Rhodophyta); Eucheuma and Kappaphycus (Zemke-White and Ohno 1999), farmed for the extraction of carrageenan; a valuable polysaccharide used as a stabilizing, emulsifying and thickening agent in food, cosmetics and pharmaceuticals.