Synthesis and Evaluation of Rice Straw Lignin Based Hydrogels as Culture Media for Growth of Pot Marigold (Calendula officinalis)

Rice straw is renewable, cost effective and abundantly available feedstock, which is usually burned on farm leading to emission of hazardous gases in North-West India. Therefore efficient utilisation of rice straw is important to reduce extensive atmospheric pollution. In the present study, rice straw was used to generate hydrogel which can be used as culture media for growth of flowering plants. The rice straw used in the study contained 20.00, 41.00, 24.00, 9.00 and 6.00 per cent composition of cellulose, hemicellulose, lignin and acid-insoluble ash (silica), respectively. Lignin from rice straw was extracted using the dilute acid pretreatment followed by its alkaline hydrolysis. Lignin was structurally characterized by FT-IR, ¹H and ¹³C NMR spectra. Hydrogels were synthesized using lignin as raw material followed by their characterization using FT-IR and SEM analysis. Different concentrations of lignin hydrogels (0.2, 0.5, 0.8 and 1.0LH) were synthesized out of which 0.5LH proved to be the most efficient due to their high swelling ratio (130.34) and high reswelling capacity. Additionally, hydrogels (0.5 and 0.8 LH) served as great culture media for seed germination and growth of marigold, which showed greater root length, shoot length, root: shoot length ratio, seed vigour index, germination percentage and germination index. Therefore, it was concluded that 0.5 and 0.8 lignin hydrogels can be used efficiently as culture media to enhance the growth of flowering plant marigold.