M. Ganesan

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

Abstract 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.

Seasonal variation in the biomass, quantity and quality of agar from Gelidiella acerosa (Forsskal) Feldmann et Hamel (Gelidiales, Rhodophyta) from the Gulf of Mannar Marine Biosphere Reserve, India

The Gulf of Mannar on the southeast coast of India, which has recently been declared as biosphere reserve, is the main harvesting place of Gelidiella acerosa for the Indian agar industry. The biomass harvested from natural stocks was estimated to be over 10 000 tonnes dry weight (DW) in the last two decades and is a serious cause of concern on long term sustainability of this valuable resource from this region. The present study reports the seasonal variation in the biomass and agar yield and quality from G. acerosa in four different habitats such as Rameswaram (rocky intertidal), Ervadi (lower intertidal), Sethukarai (subtidal) and Krusadai Island (lagoon reef area). A maximum biomass of 260 ± 26 g DW m−2 was recorded from Ervadi, whereas Sethukarai showed the highest percentage cover (69.83 ± 4.83%) and density (208.20 ± 30.16 plants m−2). Biomass, percentage cover and density were lowest in Rameswaram and significantly lower (P < 0.001) than the other three stations. A single peak in biomass was observed with autumn maxima in Ervadi and Rameswaram and southwest monsoon maxima in Sethukarai and Krusaidai Island. Length of G. acerosa was maximum (9.65 ± 0.25 cm) in Ervadi and the branch index value was maximum (24.70 ± 4.01 br−1 g−1 DW) for Rameswaram. Agar yield (37.24 ± 7.59%) and gel strength (448.66 ± 6.50 g/cm2) were higher in Sethukarai plants. The agar yields attained a peak in the northeast monsoon and decreased in summer, whereas a reverse trend was observed for gel strength. Evidently, agar yield showed a strong negative correlation with gel strength (P < 0.0001) and gelling (P < 0.0001) and melting temperatures (P < 0.01). The single annual peak in biomass observed in the present study, as compared with two peaks reported earlier, are attributed to the continuous overharvesting that would have had an effect on the overall annual biomass production. The findings of this study reveal that a single harvest during the autumn months (January to March) could yield optimum biomass with moderate agar and that would be the best for sustainable usage and conservation of this resource from this region.

Influence of ultraviolet radiation on spore liberation in marine macroalgae Ulva fasciata (Ulvales, Chlorophyceae) and Gracilaria corticata (Gracilariales, Rhodophyceae).

The effect of ultraviolet‐B (UV‐B) and UV‐A radiation on spore liberation in the intertidal marine macroalgae Ulva fasciata Delile (Chlorophyceae) and Gracilaria corticata J.Agardh (Rhodophyceae) was investigated. The two algae were exposed to UV‐A and UV‐B radiation separately for 10, 20, 30, 45 and 60 min and percentage inhibition of spore liberation was determined in controlled laboratory conditions. The spore liberation period in UV treated algae was extended for 4 days in U. fasciata and 9 days in G. corticata. UV‐B radiation inhibited spore liberation as much as 76.6% in U. fasciata and 55.5% in G. corticata at 60 min exposure. A significant positive correlation was observed between percentage inhibition of spore liberation and length of UV‐B exposure in both U. fasciata and in G. corticata. Similarly, UV‐A radiation also inhibited spore liberation as much as 75% in the former and 50% in the latter. There was a significant correlation between inhibition of spore liberation and length of UV‐A exposure in U. fasciata and in G. corticata. Analysis of variance results showed inhibition of spore liberation at 60 min of UV exposure differed significantly with that of other exposure lengths. The present findings reveal that UV‐A radiation also had an impact on spore liberation but to a lesser extent than UV‐B radiation. Thallus thickness and plant location on the shore determines their exposure to UV radiation. High UV impact was seen for U. fasciata growing in the upper parts of the intertidal region with a thin sheet like thallus and high surface area resulting in higher inhibition of spore liberation than in G. corticata.