Seaweeds are one of the important living resources of the marine ecosystem. They are the macroscopic algae that are considered as renewable sources of various bioactive compounds and produce a great variety of secondary metabolites characterized by a broad spectrum of biological activities. Fresh and dry seaweeds are extensively consumed by the people living in coastal areas as it contains carotenoids, dietary fibers, proteins, essential fatty acids, vitamins and minerals which are highly essential for human nutrition. Seaweeds have wide applications in pharmacological researches because of their antimicrobial and anti-oxidative properties. Kappaphycus alvarezii, a red alga (Division Rhodophyta), having various nutritional products including carrageenan and antioxidants, is used as food or neutraceutical supplement. They have showed effective antimicrobial activity against various human pathogens but not much is known about their antimicrobial potential for use against plant pathogens. In this study, we focused on the antimicrobial activity of Kappaphycus alvaezii against six plant pathogenic fungi (Fusarium oxysporum, Aspergillus oryzae, Penicillium chrysogenum, Phytophthoracapsici, Colletotrichumgloeosporoides, Geotrichumcandidum) and two plant pathogenic bacteria (Xanthomonas punicae and Ralstonia solanacearum). Kappaphycus alvarezii was extracted by four different organic solvents such as methanol, ethanol, acetone and chloroform. The antimicrobial activity was done by well diffusion method. In this study, we have shown that K. alvarezii hasantimicrobial potential against the tested plant pathogens. Ethanol was found to be the best solvent for extraction and retention of the antimicrobial activity of this red alga.
