Characterization of the pathogen Labyrinthula sp. isolated from the host seagrass Thalassia testudinum

The characteristic necrotic lesions exhibited by seagrass plants suffering from wasting disease are thought to be the result of infection by the pathogen Labyrinthula sp. Believed to function primarily as decomposers of senescent plant tissue, it is unknown what causes Labyrinthula spp. to become pathogenic to seagrasses. The most widely accepted hypothesis is that adverse environmental conditions contribute to wasting disease occurrences and severity. In the current study, the host specificity of Labyrinthula "T", isolated from the seagrass Thalassia testudinum, was explored. In addition, the affect of salinity on T. testudinum disease resistance mechanisms and its susceptibility to infection by Labyrinthula "T" was examined, as was the salinity tolerance of Labyrinthula "T". In contrast to previous studies, host specificity experiments demonstrated that Labyrinthula "T" isolated from T. testudinum is capable of causing wasting disease symptoms in both T. testudinum and Zostera marina. It was concluded that salinity regulates wasting disease by controlling the pathogenicity of Labyrinthula "T".