Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2017
Publication Date: 3/4/2018
Publication URL: http://handle.nal.usda.gov/10113/5898581
Citation: Shelley, B.A., Luster, D.G., Garrett, W.M., Mcmahon, M.B., Widmer, T.L. 2018. Temperature effects Phytophthora kernoviae infection, germination of sporangia and protein secretion. Plant Pathology. 67:719-728.
Interpretive Summary: A plant pathogen that has a wide host range and known to occur only in the United Kingdom and New Zealand has been found recently in Chile. Although not currently known to exist in the United States, it is a pathogen of concern due to its destructive nature and threat to valuable hosts in the U.S. Optimal conditions for the pathogen to infect the plant host are not well known. This study was done to determine the best temperature for infection and understand the infection process. Results show that there is a very narrow temperature range where infection of plant leaves occur. In addition, this pathogen secretes a protein that has been shown previously in other similar pathogens to be involved in the infection process and host response. These results provide information to regulatory agency personnel and scientists to develop risk maps that will help to predict where this pathogen may be the most likely to occur and cause disease.
Technical Abstract: Phytophthora kernoviae has been reported to cause bleeding stem lesions and foliar necrosis on a wide range of species, with little knowledge of the optimal conditions for infection. Detached Rhododendron ponticum leaves were inoculated with six different isolates of P. kernoviae sporangia and set at 10, 15, 20, 25, and 28oC. After 1 week, lesion and pathogen recovery were only observed from all isolates at 15 and 20oC and a few isolates at 10oC. The test was repeated to a more narrow temperature range of 20-25oC on R. ponticum, Magnolia stellata, and Viburnum tinus detached leaves. Lesion development and pathogen recovery occurred consistently at 20 and 21oC, limited at 22oC, and not at all at 23oC and above on R. ponticum and M. stellata, with no significant difference among any of the temperatures for V. tinus. To understand better what role temperature has on the pathogen, germination of sporangia and zoospores and mycelial growth was observed when exposed to 20-25oC. Sporangia and zoospores germinated at all temperatures, but there was a significant decrease in continued mycelial growth as the temperature increased towards 25oC (P=0.05). A crude purification of secreted proteins isolated from P. kernoviae cultures grown at 20oC produced necrosis on R. ponticum leaves while the proteins secreted from a culture grown at 24oC did not. Proteomic analysis confirmed a 10 kDa protein secreted at both 20 and 24oC shared sequence homology to the conserved domains of known elicitins of other Phytophthora spp. However, the protein secreted at 20oC that was responsible for the necrosis has not been identified.