Callus induction and thallus regeneration from callus of phycocolloid yielding seaweeds from the Indian coast

The tissue culture of phycocolloid yielding seaweeds included preparation of axenic explants, callus induction, subculture of excised callus and regeneration of plantlets from pigmented callus in the laboratory. Treatment of algal material with 0.1–0.5% detergent for 10 min and 1–2% betadine for 1–5 min and 3–5% antibiotic treatment for 48–72 h successively enabled viable axenic explants to be obtained as high as 60% for Gracilaria corticata, Sargassum tenerrimum and Turbinaria conoides and 10% for Hypnea musciformis. Callus induction was more conspicuous in T. conoides than in the other three species investigated. Of the irradiances investigated, 30 μmol photons m⁻² s⁻¹ produced calluses in as many as 40% explants in G. corticata and T. conoides and 10% in H. musciformis and S. tenerrimum. The explants cultured at 5 and 70 μmol photons m⁻² s⁻¹ did not produce any callus in all the species studied except for H. musciformis in which 10% explants developed callus at 5 μmol photons m⁻² s⁻¹. Most of the species investigated showed uniseriate filamentous Type of growths and buds from cut ends and from all over the surface of explants. Nevertheless, T. conoides had three Types of callus developments, namely (1) uniseriate filamentous Type of outgrowths from the centre of the cut end of explant, (2) bubbly Type of callus and (3) club-shaped callus clumps. The subculture of T. conoides callus embedded in 0.4% agar produced two Types of filamentous growth, namely filiform (with elongated cells) and moniliform filaments (with round cells) in the 2 months period after inoculation. Further, friable callus with loose cells was also found associated with excised callus. The moniliform filaments showed prolific growth of micro-colonies resembling to somatic embryo-like growth which, in liquid cultures, differentiated and developed into propagules with deformed shoots and distinct rhizoids. The shoots of these propagules remained stunted with abnormal leaf stalks without forming triangular shaped leaves as the parental plant and rhizoids had prolific growth in the laboratory cultures. The excised callus of G. corticata continued to grow when transferred to liquid cultures and showed differentiation of new shoots within 10 days. The shoots grew to a maximum length of 5–6 cm in the 2 months period in aerated cultures in the laboratory. Dedicated to the memory of Late Dr. Rangarajan.