Bioplastics are biobased or biodegradable plastic synthesized from natural resources with similar features to conventional plastic and environmental sustainability. Seaweed species abundant in the coastal regions of Bangladesh are yet to be explored for developing biodegradable plastic to solve the plastic pollution problem. Semi-refined kappa carrageenan was extracted from Gracilaria sp. with Pressurized Hot Water Extraction (PHWE) and blended with sorbitol and polyethylene glycol 1540 in this study, respectively. The presence of carrageenan and other functional groups was confirmed with FTIR analysis. The bioplastic films showed over 90 % biodegradability after 16 days of soil burial test and 98 % water solubility after immersion for 16 days. Maximum 20 MPa tensile strength and 44 % elongation were observed from the bioplastic films. The polyethylene glycol 1540 blended films showed better physical and mechanical properties. SEM analysis was conducted to evaluate the influence of tensile strength and elongation on the surface integrity of the bioplastic films. The findings indicate that Gracilaria sp. found in the coastal regions of Bangladesh, can be a potential candidate for developing bioplastics for food packaging and many other applications.

Seaweed extracts from Sargassum cristaefolium at 10% concentrations, effectively inhibited the mycelial growth of Colletotrichum gloeosporioides. According to the available literatures, the GC-MS analysis identified various compounds in these extracts that had a antifungal, antibacterial and antioxidant properties as per previous report. In both pot culture trials and field settings, the application of seaweed extracts via bulb treatment, soil drench, and foliar spray resulted in a notable decrease in the occurrence of twister blight disease. Among the treatments, treatment three, involving bulb treatment with S. cristaefolium at a 10% concentration, soil drench with the same seaweed at a 10% concentration and foliar application of S. cristaefolium at a 10% concentration, demonstrated a remarkable 69.39% reduction in twister blight, showcasing efficacy comparable to biocontrol agents and chemical fungicides. In pot culture conditions, increased levels of peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase were observed, suggesting their involvement in enhancing resistance against disease. Histopathological examinations further revealed reduced tissue damage in treated plants. Additionally, protein content in both leaves and bulbs exhibited an increase in treated plants. This comprehensive study not only underscores the potential of seaweed extracts as effective biostimulants for disease management but also highlights their positive influence on overall plant health and productivity.