3.2.2 Gracilaria – Agar Industry
Gracilaria is a red algae notable for its economic importance as a source of agar (more than 70 per cent of the raw material worldwide), bioactive compounds, as well as a food source for humans and various species of shellfish. Several species within the genus, including G.chilensis (a) and G.gracilis (b) are exploited among Asia, South America, Africa and Oceania, in wild or planted seaweed beds.
Similarly to Kappaphycus, Gracilaria farms are plagued by epiphytes that hamper productivity and decrease the market value of the crop. Overall the majority of those epiphytes also belong to the order Ceramiales, including Ceramium minuta, and Polysiphoniaforfex (Munoz et al., 2009 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] )
Reports on diseases affecting Gracilaria beds are scarce and no terminology has been yet defined to describe specific symptoms (and there are no pictures available to date). Nevertheless, recurrent die-offs of Gracilaria gracilis in production facilities established positive correlations between disease symptoms (‘white-tip’ and ‘rotten-thallus’ syndromes) and the occurrence of epiphytic agarolytic bacteria (Schroeder et al., 2003). Among those, Pseudoalteromonas species are well represented, and were also associated with G. cordicata ‘Bleaching Stripe Disease’. A recent minireview of Egan et al., (2013) provides a list of confirmed and putative bacterial pathogens of macroalgae, some of which attacking Gracilaria.
In Hawaii, farmers and researches reported the Gracilaria Gall syndrome affecting G. tikvahiae. The disease slows or stops growth, reduces shelf-life and disfigures the seaweed, making it difficult to market. Diseased thalli display abnormal lesions or galls (small bump-like structures) along their stems or branches. Growth beyond the gall becomes twisted or contorted, and ‘witch’s-broom’-like structures may also appear at the ends of the branches. Research efforts were also focused on bacterial causative agents, but no further reports have been published since 1996.
3.2.1 Kappaphycus – Carrageenan Industry