DEGRADATIVE DISEASE IN ULVA-RIGIDA (CHLOROPHYCEAE) ASSOCIATED WITH ACROCHAETE-GENICULATA (CHLOROPHYCEAE)

A destructive disease affecting tank-cultivated Ulva rigida C. Agardh. was characterized by green spots, initially located at the base of th e thalli, that spread through the host thallus and gradually caused pe rforations of the frond. The endophytic filamentous green alga Acrocha ete geniculata (Gardner) O'Kelly was identified as the causative agent of the disease. The effects of this infection on the host varied from minor injuries to gross frond destruction. Advanced stages of infecti on resulted in frond wrinkling and severe tissue loss. These symptoms were caused by a primary compaction of the host cells due to a direct effect of the endophyte followed by secondary bacterial infections tha t became part of the degradative process initiated by the algal pathog en. Co-cultivation of healthy and diseased fronds resulted in transfer of the infection within 2 weeks; however, attempts to infect the host in the laboratory with actively reproducing suspensions of the endoph yte were unsuccessful.