Wart-like spot formation on the fronds of Chondrus ocellatus (Gigartinales) by a brown alga, Mikrosyphar zosterae (Ectocarpales) in Korea

A brown filamentous endophyte, Mikrosyphar zosterae, occasionally appears as an epiendophyte of seagrass in Europe and North America. In the present study, M. zosterae was first isolated from wart-like spots of the red alga Chondrus ocellatus and identified by morphological features and molecular analysis. The production of wart-like spots M. zosterae on the host C. ocellatus fronds was confirmed using Koch’s postulates and in mixed culture of the two species. Neither hypertrophic nor hyperplastic cells of host C. ocellatus were found in the wart-like spots which differed from gall composition in other species. Wart-like spot formation by brown filamentous M. zosterae on the red macroalgal fronds is reported for the first time. In the culture, three morphological types of M. zosterae were observed, which were heterotrichous, pseudoparenchymatous and monostromatic prostrate thalli. Phaeophycean hairs and reproductive organs (both unilocular and plurilocular sporangia) of M. zosterae were also observed in the culture. In conclusion, M. zosterae is a causative agent producing wart-like spots on Chondrus fronds, which is a new record in red seaweeds and was confirmed in the laboratory culture for the first time.