Observations on the pathology of seaweeds in the Pacific Northwest

Seaweeds that displayed disease symptoms were collected intertidally and subtidally from coastal Washington and British Columbia. A red rot of Fucus, characterized by the progressive reddish discoloration and ultimate disintegration of host tissue, was observed frequently. The fungus Cephalosporium was isolated consistently from diseased plants. Extensive galls, from 1 to 50 mm in size, on stipes of Laminaria, Nereocystis, and Macrocystis, were associated invariably with a filamentous, endophytic, and presumably parasitic Streblonema-like alga. A bacterium, identified tentatively as Acinetobacter, was isolated from infected Nereocystis in the laboratory and shown to be pathogenic by fulfillment of Koch's Postulates. Symptoms or signs of this white rot disease were restricted to exposed, floating stipes and pneumatocysts which collapsed, became flaccid, and were covered with a white bacterial slime. Attempts to demonstrate causality with the putative pathogens causing red rot and galls, respectively, were unsuccessful. Nematodes of the genera Paralinhomeous and Monhystera were isolated from Fucus and Laminaria, respectively, but appear to be free-living and not parasitic.