Executive Summary : | Seaweed farming – A fast-growing sector: Macroalgae, aka seaweeds, have long been considered a source of nutrition, livestock feed, fertilizer, and medicine. Kappaphycus alvarezii is the only species of red seaweed widely cultivated in India to produce carrageenan for commercial use. National importance: The launch of Pradhan Mantri Matsya Sampada Yojana by Govt. of India sets an aggressive mission of producing 10 million metric tonnes of fresh seaweed feedstock in 5-years (Mantri et al. 2022) has reignited attention to this study. From 2001 to 2013, India's production of K. alvarezii substantially increased, from 21 to 1490 dry tonnes. Later on, due to environmental factors and diseases, production declined drastically (Mantri et al. 2017). In the last decade, seaweed cultivators have been trying to achieve production as did farming before 2013 on Tamil Nadu coast. The leading cause of diseases is the influence of extreme environmental variables that exceed seaweed's threshold, such as exposure to extreme light intensity, low water salinity, and nutrient deficiencies, which end up causing seaweeds to become more susceptible to infectious diseases by bacteria, fungi, viruses and protozoans. Therefore, it is crucial to study by isolating, screening and identifying the causative pathogens to diagnose and control seaweed diseases. The most predominant diseases in seaweeds are chytrid blight, white spot, red rot, diatom felt, green spot, hole-rotten, shot hole, and blister caused by pathogenic bacteria (Behera et al. 2022). As seaweed farming advances along the Indian coast, it's becoming more critical to morphologically identify the possible pest and disease concerns to develop disease control techniques. Preliminary work done and rationale for the proposed objectives: According to the aforementioned facts, research has begun to investigate and identify bacteria in diseased K. alvarezii samples collected from various cultivation sites. Culture-independent (16S rRNA gene sequencing) and -dependent cataloguing of bacterial diversity through molecular approaches, metabolomic and phytocompound screening of diseased and healthy seaweed samples collected from farming sites was commenced. Found a set of 25 isolates, purified and maintained glycerol stocks, and re-infected the healthy seaweed samples in vitro conditions to see the pathogenicity and impact on seaweed growth and survival. This study aims to identify the disease-causing pathogenic bacteria through 16S rRNA gene sequence and morphological and biochemical characteristics to develop remedies and control mechanisms using natural compounds. Our findings may not only aid in developing a robust experimental model among pathogens and seaweed to understand pathogenesis better. The study will also disclose the information for disease prevention to avoid and moderate its severity effectively. Hence, as a pioneering effort, this study can effectively be utilized for other economically important seaweeds. |