The effects of agar concentrations on growth and callus formation were studied in axenic cultures of female gametophytes of green and red morphs of Gracilaria domingensis (Kützing) Sonder ex Dickie. Unialgal cultures of both color morphs were maintained in sterilized seawater (30-32 psu) enriched with a quarter-strength of von Stosch’s solution (VSES 25%), 22 ± 2 ºC, photoperiod of 14 h, irradiance of 50-80 µmol photons m-2 s-1. To obtain axenic explants, apical and intercalary segments of the green and red morphs were cultured for 48 h in VSES 25% medium with addition of antifungal and antibiotic solution, washed with a solution of sterile seawater with 0.5% of sodium hypochlorite and 200 µL L-1 of detergent during 20 seconds. In order to evaluate the effects of agar, apical and intercalary segments were inoculated into modified ASP 12-NTA synthetic medium with agar concentrations ranging from zero to 1.0%. Addition of agar to the culture medium inhibited the growth of apical segments of both morphs as well as the growth of intercalary segments of green morph. In general, growth rates of thallus segments were inversely proportional to agar concentration. Treatments with agar induced the formation of three types of callus, denominated in accordance with the explant region which gave rise to the callus: apical, basal, and intermediate calluses. Moreover, presence of agar is essential to induce intermediate and apical calluses. Concentrations of 0.5% and 0.7% of agar were the optimal values for the induction of basal and intermediate calluses of greem morph, respectively. The results indicated that agar has a regulatory role on morphogenetical processes in color morphs of G. domingensis.
agar; callus; color morphs; Gracilaria domingensis; Rhodophyta
