The effects of the environmental factors on Laminaria disease caused by alginic acid decomposing bacteria

The rot disease of Laminaria occurs often in nurseries of sporeling and commercial cultivation in the sea and results in economic loss greatly.Usually the disease outbreaks accompanied with massive multiplication of alginic acid decomposing bacteria.From the section of the decaying Lamuutria which resulted from the inoculation of alginic acid decomposing bacteria,it was observed that the bacteria invaded the epiderm of the Laminaria surface at first,then entered the ex-odermis,endodermis and pith.In addition,there were a great amount of bacteria in the intercellular region and a lot of free cells of the algae in the decaying areas.The wall of some free cells was decomposed,which led to soft tissue or disintegration.Alginic acid decomposing bacteria are normal epiphytic microorganisms growing on Lamuutria surface.These bacteria do not cause disease at normal environmental conditions.The experiments showed that the unfavourable conditions,e.g.,wounding,overcrowding,high temperature reduced the ability of antibacterial activity and made the algae more susceptible to the pathogens and favoured the multiplication of alginic acid decomposing bacteria and finally led to the disease outbreat.1le unfavourable environmental factors which resulted from a variety of reasons were the main cause of the disease.