Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2017
Publication Date: 1/6/2018
Publication URL: http://handle.nal.usda.gov/10113/5887315
Citation: Widmer, T.L., Tooley, P.W., Camp, M.J. 2018. Recovery of Phytophthora ramorum in plant tissue with mixed infections. European Journal of Plant Pathology. 150:253-258.
Interpretive Summary: Fungal-like organisms can cause serious diseases on plants. In order to best manage and limit spread of these diseases, it is important to identify the organism that is causing the disease. However, sometimes plants are infected by more than one type of organism but it may be difficult to separate and identify both organisms. In this study, it was determined that when two different species of a fungal-like organism in the same genus were applied to a host plant, recovery of both organisms was not always possible. The host plant itself was important in being able to detect or not detect both organisms. This is important because if only one organism is detected but the other one is present, then the one not detected may be unknowingly spread to new areas. This will be very important to those agencies that monitor and regulate the spread of plant pathogens.
Technical Abstract: This study was performed to investigate the frequency with which P. ramorum would be isolated from host tissue co-infected with P. ramorum as well as an indigenous Phytophthora species or P. kernoviae. Three separate experiments were tested in a similar manner using different combinations of pathogens and hosts. Overall for any of the individual experiments, very few segments did not have any growth of Phytophthora spp. For mixed infections of P. ramorum and P. kernoviae, a difference was observed between isolating both of the species and P. ramorum only on rhododendron. The data showed that P. ramorum or P. kernoviae will not be detected 29 or 12 percent of the time, respectively, in infected Rhododendron sp. Phytophthora kernoviae was not detected alone in mixed infections with P. ramorum on Pieris japonica. When two different P. ramorum isolates were co-inoculated individually with one P. citricola isolate, there was a significant difference between isolating P. ramorum and isolating both species. These results confirm that choice of host species used for baiting can strongly influence detection results. For example, if P. japonica were used for baiting in mixed infections, there is a 55 percent chance that P. kernoviae would not be detected. This study highlights the difficulty in being confident in isolating and identifying an individual Phytophthora sp. from host material when mixed infections are present, and emphasizes the importance of a large sample size in order to increase the chances to recover all possible different species in a mixed infection.