Detection methods for Phytophthora fragariae
1) Detection and identification by PCR
Red core of strawberry and raspberry root rot are respectively caused by Phytophthora fragariae var fragariae and by P. fragariae var rubi (both EPPO A2 quarantine pests). Infection can be difficult to detect, especially in summer when the fungus is largely inactive and is present principally as oospores. Other Phytophthora species (e.g. P. cactorum) may also affect plants but are not subjected to quarantine measures. Therefore, there is a need for highly sensitive and discriminatory tests to detect low levels of infection of P. fragariae. A PCR technique has been developed in the Netherlands and Scotland. Sequences of the internal transcribed spacer region of the ribosomal gene repeat (rDNA) were used to develop specific primers in a nested-PCR. With this technique, it was possible to detect specifically P. fragariae in infected but symptomless roots, and also to detect zoospores in contamined water samples. The method is highly sensitive, and is at least as sensitive as the bait plant test. Although this work was mainly done on P. fragariae var. fragariae, the PCR method can also be used for P. fragariae var. rubi.
2) Detection of Phytophthora fragariae var. rubi by ELISA
A commercial ELISA kit (ELISA multiwell Kit E developed by Agri-Diagnostics Ass., USA) for the detection of Phytophthora spp. was studied in order to: 1) evaluate the earliest time after zoospore inoculation at which this kit can detect a latent infection of Phytophthora fragariae var. rubi in raspberry plants, 2) find the detection limit of the kit (small amounts of infected raspberry root mass were mixed with healthy root mass in simulated infections). When root systems of raspberry plants were inoculated with zoospores of Phytophthora fragariae var. rubi, the pathogen could be detected in extracts already 4 days after inoculation. For simulated infections, where 0.25, 0.5, 1.0 and 1.5% infected tissues were mixed with healthy tissues (w/w), it was possible to detect the pathogen at 0.25% of simulated infection level. The authors felt that this ELISA test offers better possibilities for an early diagnosis of Phytophthora diseases of raspberry and therefore for a more effective control of these diseases, in preventing their spread on latently infected planting material.
Bonants, P.; Hagenaar-de Weerdt, M.; van Gent-Pelzer, M.; Lacourt, I.; Cooke, D.; Duncan, J. (1997) Detection and identification of Phytophthora fragariae Hickman by the polymerase chain reaction.
European Journal of Plant Pathology, 103(4), 345-355.
Olsson, C.H.B; Heiberg, N. (1997) Sensitivity of the ELISA test to detect Phytophthora fragariae var. rubi in raspberry roots.
Journal of Phytopathology, 145(7), 285-288.