Effects Of Temperature On Germination Of Sporangia, Infection And Protein Secretion By Phytophthora Kernoviae

Phytophthora kernoviae is a pathogen on a wide range of plants, but little is known of optimal infection conditions. Rhododendron ponticum leaves were inoculated with six different isolates of P.kernoviae sporangia and incubated at different temperatures from 10 to 28 degrees C. After 1week, lesion development and pathogen recovery were only observed from all isolates at 15 and 20 degrees C and a few isolates at 10 degrees C. In an experiment with temperatures ranging from 20 to 25 degrees C, lesion development and pathogen recovery on R.ponticum, Magnolia stellata and Viburnum tinus occurred consistently at 20 and 21 degrees C, was limited at 22 degrees C, and did not occur at 23 degrees C and above. There was no difference in sporangia and zoospore germination at 20-25 degrees C. In a temperature fluctuation experiment, the necrotic area of inoculated R.ponticum leaves increased with longer incubation at 20 degrees C and decreased with longer incubation at 24 degrees C. Crude extracts of secreted proteins from P.kernoviae cultures grown at 20 and 24 degrees C were compared to determine any effects of temperature on pathogenicity. When spot tested on R.ponticum leaves, crude protein suspensions from cultures grown at 20 degrees C induced necrosis, while proteins from cultures grown at 24 degrees C did not. Proteomic analysis confirmed that a 10kDa protein secreted at both 20 and 24 degrees C shared sequence homology to the conserved domains of known elicitins of other Phytophthora spp. The protein secreted at 20 degrees C that was responsible for necrosis has not been identified.