Use of plant growth regulators in micropropagation of Kappaphycus alvarezii (Doty) in airlift bioreactors

The effects of plant growth regulators on callus induction rate and regeneration of K. alvarezii explants was evaluated.K. alvarezii calluses were induced in vitro with kinetin (K), 6benzylaminopurine (B), 1-naphtalene acetic acid (N) and spermine (S). After 30 days, K. alvarezii explants produced filamentous calluses and isolated crystalline filaments growing from the medullar region and from cortical cells at the cut edge. The plant growth regulators 1-naphtalene acetic acid (1 mg L−1) and 6-benzylaminopurine (1 mg L−1) and the 1-naphtalene acetic acid + kinetin + spermine (1, 1, 0.018 mg L−1 respectively) combination produced 85 to 129% more calluses, with significant differences versus the control (p < 0.05). Spermine at 0.018 mg L−1 produced calluses in the apical, intercalary and basal regions of explants. Spermine also reduced callus induction time to 7 days, which is faster than previously reported induction times with other plant growth regulators. An airlift bioreactor was designed and characterized to micropropagate K. alvarezii calluses. The bioreactor had mixing times ranging from 4.6–10.3 s at T90 and T95, which is shorter than those for the Fernbach (5.2–13.4 s) and balloon flasks (6.3–17.3 s). Mixing time standard deviations were smaller for the bioreactor (1.1–4.6) than for the Fernbach (9.3–13.6) and balloon flasks (5.5–15.8), suggesting an adequate flow regime within the bioreactor. The results are useful for improving callus induction in K. alvarezii and propagating microplantlets in an airlift bioreactor, and provide baseline data for macroalgal bioreactor culture