Description of a white spot disease of field cultivated kelp (Saccharina japonica) and evaluation of its influences on the growth and phytochemical contents

Abstract

Diverse diseases have been causing the serious biomass and economic losses of cultivated kelp, Saccharina japonica. In this study, we described a prevalent kelp disease, white spot disease, which was found in northern China in recent years, and evaluated its influences on kelp growth and phytochemical contents. The disease sustained a period from the fast-growing to the harvest of kelp, prevailing generally from March to May. The diseased kelps were scattered with irregular white spots in different sizes in the upper and middle parts of sporophytes, which were accompanied occasionally with blisters exceeding 10 cm as the maximum diameter. The medulla of diseased sporophytes became loose, but no change was found in their epidermis and cortex. White spot disease caused a loss of daily increase of sporophyte length by 42 % when it was intense. One to two thirds of diseased sporophytes self-healed up to some extent. The self-healed sporophytes recovered normal color, their white spots gradually disappeared and their daily increase of sporophyte length returned to that of the healthy ones. The self-healing of diseased sporophytes aided to recover the yield and quality of kelp products. However, the blisters tended to be residual and sometimes white spot reappeared in newly generated tissue of the self-healed sporophytes. The disease caused less accumulation of pigment with the growth of S. japonica, but more increases of total phenolic content, DPPH radical-scavenging activity and reducing power with an exception in June. The disease also affected iodine and crude protein contents, but not ash, mannitol, alginate and crude fucoidan contents.