Population dynamics of Meloidogyne chitwoodi and M. fallax (MELOPOP)

We still lack critical information on the spread of Meloidogyne spp. and especially the quarantine species M. chitwoodi and M. fallax in Europe and on the characteristics of the various populations. There is a need to standardize survey methods for detection of M. chitwoodi and M. fallax and to relate the current spread to parameters such as soil characteristics, climate and crop rotation practises. It is also important to know whether the current populations can be subdivided into different races or pathotypes. The initial objectives of the current study were 1) to perform a survey based on a standardized sampling protocol, 2) to monitor populations in the field for multiple years, and 3) to characterize M. chitwoodi and M. fallax populations using bioassays. Germany, France, Belgium, Turkey, Slovenia and the Netherlands participated in the project.

Consensus on survey was lacking and the objectives 1 and 2 were abandoned. Only one country performed the envisioned survey as planned. Populations that had previously been detected in the participating countries and whose origin is not disclosed, were used for biological and molecular characterisation. Only M. chitwoodi populations were tested in the bioassay using a reference population M. chitwoodi called ‘Smakt’ and with prescribed plant material (differentials, according to Brown et al, 2009).

The bioassay on Meloidogyne populations in four countries showed that it is difficult to stick to a uniform workflow despite of the presence of a standard protocol. Given these circumstances, we cannot be sure whether differences in host response are related to biological relevant differences or whether they result from differences in experimental procedures. However, the main question was to determine whether different races and/or pathotypes are present in the participating countries. This question was translated into the simple question of whether the populations differed from the reference population ‘Smakt’ on the set of differential host species per country. It remains debatable whether results on the response to Meloidogyne should be expressed in Pf-values or Pf/Pi values. The reference population reproduced on tomato, the susceptible potato cultivar and (to a lesser extent) on carrot. This population displayed Pf/Pi values <1 on alfalfa and the resistant potato. This pattern is typical for host race 1 of M. chitwoodi. All other test populations display a pattern that is highly similar with minor inconsistencies and a few inconclusive results.
While noting the shortcomings that arise from variation in the applied methods, we conclude
that all tested populations from Europe most likely belong to race 1 of M. chitwoodi. The molecular characterisation of the different populations within Europe still has to take place, but the difficulty that the currently available markers do not show high levels of polymorphism are in agreement with the bioassay results.
These findings are relevant for plant health management as control of these nematodes by using resistant crops, which is one of the few options, will become more straightforward. This underlines the need for crops that are resistant against M. chitwoodi from host race 1.