Genetic studies on Meloidogyne chitwoodi and M. fallax
Reliable differentiation methods between Meloidogyne chitwoodi, M. fallax (both EPPO A2 quarantine pests) and other Meloidogyne species are needed for quarantine purposes. In particular, both M. chitwoodi and M. fallax live in the same environment as M. hapla. A molecular technique (ITS-RFLP) was used to compare 3 German populations of M. chitwoodi (sensu lato, as these populations were found before M. fallax was described as a separate species) to populations of the same species from the Netherlands and USA, and to 5 other Meloidogyne species (M. fallax, M. hapla, M. naasi, M. incognita, M. javanica). With this technique, clear differentiation was obtained between M. chitwoodi, M. fallax, M. hapla, M. naasi, and the group M. incognita/M. javanica (to differentiate these two species other restriction enzymes had to be used). As a result, two German populations were assigned to M. chitwoodi and one population to M. fallax.
Genetic relationships between these Meloidogyne species were also studied by using RADP analysis. A clear separation was observed between all species investigated, with the smallest distance between M. incognita and M. javanica. A close relationship was found between M. chitwoodi and M. fallax but the species are clearly distinct. M. chitwoodi populations could also be classified approximately according to their geographic origins. On the basis of genetic distances between nematode populations from USA, Germany and the Netherlands, an introduction of M. chitwoodi from USA to Germany or to Netherlands appears unlikely, as well as an introduction from the Netherlands to Germany. The present distribution of M. chitwoodi in Europe suggests that populations of M. chitwoodi and M. fallax have existed for a long time in Europe. The authors felt that further studies on additional populations are necessary, but stressed that this no longer possible with German populations, because in spite of extensive searches in different regions of Germany, M. chitwoodi and M. fallax could no longer be found.
Note: In 1998, the German NPPO has officially declared that M. chitwoodi was found in the past but not established in Germany.
Sources
Schmitz, B.; Burgermeister, W.; Braasch, H. (1998) Molecular genetic classification of Central European Meloidogyne chitwoodi and M. fallax populations.
Nachrichtenblatt des Deutschen Pflanzenschutzdienstes, 50(12), 310-317.