Study on the cause investigation and how to relieve the development of disease and discoloration in cultivated laver in Ise Bay [Japan]

The laver farming is one of the most important fishing industries in Ise Bay. However, recently the production has been seriously affected by the disease outbreaks and other physiological damages. In particular, the laver farming is severely damaged by red rot disease induced by Pythium porphyrae and discoloration induced by lack of nutrients every year. The purpose of this study is to investigate the cause of development of red rot disease and discoloration disorder in order to impart stability to laver farming in Mie Prefecture and to suggest strategies to prevent their occurrences. At first, sea conditions were compared and analyzed against the disease and the disorder using a geographical information system (GIS) in order to find relationships between them. For this purpose, monthly average sea conditions which were determined using ecological data during the period of the laver farming of the past twenty years and outbreak of serious red rot disease and discoloration during the same period were analyzed using GIS. It was found that the potential dangerous time and area of red rot disease and discoloration could be roughly estimated by GIS analysis. Secondary, infection by zoospores released into seawater from zoosporangium is one of the important factors associated with the spread of disease. However, no data on the density of the zoospores in seawater was available and the zoospore concentration in the laver culture farm at the time of disease outbreak was not known. Therefore, in the present study, production of the specific monoclonal antibody recognizing only the disease germ P. porphyrae was tried, and the method to measure the zoospore concentration in the seawater was developed. Consequently, the cell fusion between the spleen cells which were immune to the red rot causative pathogen and mouse myeloma cell was performed, and a highly specific monoclonal antibody product cell which reacted only to the red rot causative pathogen was successfully produced. Furthermore, the detection method of the causative pathogen in the seawater using this antibody was established, and as a result it was possible to observe the increase and decrease in the causative pathogen population in the laver culture farm. This method could detect the causative pathogen before l2 days, to compared with the first time naked eye visibility of the disease. Furthermore, when the density of zoospores of the causative pathogen in seawater was between 10(2)-10(3) cells per liter, it became clear that the risk of the red rot disease was high. As a result, the possibility of forecasting of this disease was shown.