Apical, sub-apical, and basal explants of industrially exploited marine red alga Gracilaria salicornia exhibited differential response to commercial seaweed-derived plant bio-stimulants

The cultivation of the red algal genus Gracilaria is successful and accounts for a ca. 14% global share in farmed seaweed. Gracilaria salicornia has been used as feedstock for commercial production of galactans and plant bio-stimulant. The un-abated demand of raw material during last 5 years by domestic industries has fueled ca. 757% increase in biomass exploitation of this resource. As the farming methods heavily rely on clonal propagation of apical explants, it is imperative to check the viability of sub-apical and basal explant to increase the number of clones needed for farming operation. Here we ascertained the efficacy of two commercially available seaweed-derived plant bio-stimulants namely AMPEP and Sagarika under various concentrations and treatment times. One hundred percent survival was recorded with 0.1% AMPEP and 15-, 30-min exposure, 10% AMPEP and 15-, 30-, and 60-min exposure, while with Sagarika, it was observed in 0.01% and 60 min, 0.001% and 15, 30, and 60 min and 0.1% and 30, 60 min treatments of apical explants. The highest regeneration of 80.42 ± 12.01% was observed in apical explants at 1% AMPEP and 15-min exposure and the highest growth of 3.66 ± 0.32% day⁻¹ was found in apical explants with 1% AMPEP and 60-min exposure. The proximate composition of apical explants treated with 0.1 g L⁻¹ AMPEP and 60-min exposure was 25.10 ± 3.9% carbohydrate, 13.59 ± 4.8% protein, and 4.6 ± 1.1% lipid, while total phenol and free radical activity were 13.11 ± 1.65% and 37.93 ± 1.9%, respectively. Although apical explants clearly showed superiority for clonal propagation, use of sub-apical and basal explants can also be considered for commercial seedlings production in case of paucity of material to continue the operation. The sustainable production of seedlings would help in negating consequences of natural harvesting while ensuring continuous feedstock supply through cultivation.