The host – pathogen interaction in the wasting disease of eelgrass, Zostera marina

A marine epidemic of wasting disease decimated populations of eelgrass, Zostera marina L., in the early 1930s. Labyrinthula, a marine slime mold was the suspected pathogen, although the cause was never clearly determined. Presently, a recurrence of wasting disease of Z. marina was documented in populations along the coasts of North America and Europe. A pathogenic species of Labyrinthula, described as Labyrinthula zosterae Porter et Muehlstein, was identified as the primary microorganism causing the present wasting disease. Of all the microorganisms tested in laboratory disease tests, only L. zosterae caused disease symptoms. Direct microscopic observations revealed that Labyrinthula cells were found most frequently associated with marginal areas of disease symptoms and appeared to move rapidly through the tissue, directly penetrating cell walls. The ectoplasmic network that surrounds Labyrinthula cells appeared to have an important role in the enzymatic degradation of plant cell walls and presumably a role in the destruction of cytoplasmic contents of the plant cells. Direct contact of diseased leaves with healthy leaves was the mechanism of disease spread from plant to plant. Key words: Labyrinthula, Zostera marina, eelgrass wasting disease.