Real-time PCR to detect Phytophthora ramorum
A real-time PCR assay was developed in California (US) to detect and quantify Phytophthora ramorum (EPPO Alert List). This method was found sensitive (it can detect less than 12 fg of pathogen DNA) and specific (it did not react with 21 other species of Phytophthora). However, it gave some cross-reactions with P. lateralis under certain circumstances (high DNA concentrations). As P. lateralis has a completely distinct host range, it was considered that this should not cause problems in practice. This PCR assay has been used for a state-wide survey and results are given for the period from May 2001 to August 2002 (the survey is still continuing). Using this method, the presence of P. ramorum was detected in 4 new counties in California (Contra Costa, Humbolt, Mendocino and Solano). This assay also allowed detection of P. ramorum on new host plants (Acer macrophyllum, Aesculus californica, Arbutus menziesii, Arctostaphylos manzanita, Heteromeles arbutifolia, Lonicera hispidula, Rhamnus californica, Rhododendron macrophyllum, Sequoia sempervirens, Umbellularia californica). These PCR-based discoveries were then confirmed by traditional pathogen isolations and inoculation studies. First data on seasonality of the pathogen was also obtained with this method. The highest
frequency of detection was obtained from March to June, which suggests that surveys for P. ramorum in California are best carried out in late spring.
Sources
Hayden KJ, Rizzo D, Tse J, Garbelotto M (2004) Detection and quantification of Phytophthora ramorum from California forest using a real-time polymerase chain reaction assay.
Phytopathology, 94(10), 1075-1083.