Tissue culture and regeneration of thallus from callus of Gelidiella acerosa (Gelidiaies, Rhodophyta)

The tissue culture of an economically important red alga Gelidiella acerosa (Gelidiales, Rhodophyta) included preparation of axenic material, culture of explants, subculture of excised callus and regeneration of de novo plants from callus in the laboratory. Sequential treatment of explants with sterile seawater consisting of 0.1% liquid detergent for 10 min, 2% betadine (with 0.5% w/v available iodine) for 5 min and 3.5% broad-spectrum antibiotic mixture with nystatin for 2 days enabled yields as high as 90% of viable and axenic explants. A prolific and rapid growth of filamentous callus on explants was observed on cut surfaces during the first month of culture. The highest level of callus induction occurred in Provasoli enriched seawater (PES) medium solidified with 1.5% agar incubated at 20–22°C and a photon flux density of 5 μmol photons m⁻² s⁻¹ with a 12: 12 light-dark photoperiod. Up to 90% of the explants cultured at 5 μmol photons m⁻² s⁻¹ produced callus, whereas at 30 and 70 μmol photons m⁻² s⁻¹, 70% and 9% produced callus, respectively. The explant culture medium with 0.5% agar content stimulated bud development in all explants, whereas higher agar concentrations (0.8%, 1.0%, 1.5%, 2.0% and 3.0%) resulted in a filamentous type of callus growth. Addition of the plant growth regulators naphthalene acetic acid and indole 3-acetic acid (auxins), and benzyl amino purine and kinetin (cytokinins) and different organic carbon supplements (glycerol, sucrose, sorbitol and mannitol) to the culture medium had no effect on callus growth or induction rate. All carbon supplies at 0.5 and 1.0 M concentration showed an inhibitory effect and most of the explants perished gradually after 2 weeks in culture. The callus mass with bud or shoot developments continued to grow when transferred to semisolid PES medium (0.2% agar w/v) on a rotary shaker. In 4 months, these shoots gave rise to 2–3 cm long plantlets of G. acerosa. The tissue-cultured Gelidiella germlings were successfully grown into full plants in the field on coral stones in 6 months.