The host-range of Paraphysoderma sedebokerensis, a chytrid that infects Haematococcus pluvialis

A parasitic chytrid that attacks the green alga Haematococcus pluvialis was recently isolated in our laboratory and identified as a novel species from the phylum Blastocladiomycota, named herein Paraphysoderma sedebokerensis (nom. prov.). A method for early and precise detection of chytrid infections was developed using the fluorescent dye, Nile red, which stained the chytrids' sporangia. Using this technique we determined the specificity of Paraphysoderma sedebokerensis for 13 algal species belonging to the Chlorophyta. Algal species tested including: Chlamydomonas nivalis, Chlorella emersonii, Chlorella vulgaris, Chlorococcum sp., Chlorogonium elongatum, Monoraphidium braunii, Muriella zofigiensis, Scenedesmus obliquus, Scenedesmus vacuolatus (two strains), and Scotiellopsis oocystiformis were either resistant to infection, or only experienced slight levels of infection during exponential growth. During exponential growth phase 100% Chlorella zofigiensis Donz cells were infected, but none developed any infection during resting stage. Only in cultures of H. pluvialis did infections develop rapidly (3-4 days) and intensively (100% cells infected) during both the logarithmic and stationary stages of growth. We suggest that the newly isolated chytrid, Paraphysoderma sedebokerensis (nom. prov.), is highly specific for H. pluvialis, but has a limited capacity to infect other green algae.