Effect of duration of culture period on the agar yield and gel strength of Gracilaria dura C. Agardh (Gracilariaceae, Rhodophyta) at Saurashtra coast, Gujarat, India

Abstract Gracilaria dura J. Agardh is a promising source of agar and agarose and have potential for commercial farming in India. Due to moderate to strong wave action along the west coast of India, the tube-net and floating monoline methods are recommended for commercial cultivation of G. dura. In order to optimized the culture period, for augmented biomass production and better quality of agar, G. dura was cultivated by floating monoline method with different culture period such as 15, 25, 35, 45 and 55 days cycle− 1 during December, 2018 to April, 2020. It was observed that the Daily Growth Rate (DGR), progressively decreased with increase in the duration of culture period. Among the culture period analyzed, the highest DGR (8.47 ± 2.29%) and biomass yield (233.3 ± 82.48 g.fr.wt m− 1) was observed at 15 and 35 days culture period respectively. Both biomass yield and DGR significantly (p < 0.05) varied between growth period tested. Higher agar yield (34.5 ± 0.71%) and gel strength (1606.5 ± 27.58 g cm− 2) was recorded at 35 days and 25 days culture period respectively. However, gel strength did not vary significantly (p > 0.05) between different culture periods and agar yield, whereas the ash content was varied significantly (p > 0.05) between different culture period. Minimal culture period maintained the vegetative phase of G. dura and reducing the maturity (i.e. sporulation phase) which resulted higher biomass yield and DGR. Harvests cycle also reduced while increasing culture period. Therefore, the culture period of 25–35 days was found ideal for commercial farming of G. dura along the Saurashtra coast, India.