Interesting findings of root-knot nematodes (Meloidogyne spp.) in samples for nematode diagnostics

The Diagnostic Centre for Plants at ILVO is the National Reference Laboratory (NRL) for plant nematology in Belgium. We receive about 1500 samples annually for nematode detection and identification. Half of the samples are brought in by the National Plant Protections Service (FAVV) and consist of soil samples taken in fields and nurseries, and from plants and substrates in international trade. The other half are mainly soil samples brought in by growers. In 2012, 8 % of the samples contained juveniles of root-knot nematodes, Meloidogyne sp., of which 15% from field crops, 26% from vegetable crops and 32% from fruit orchards. The most common species encountered were M. naasi, the grass root-knot nematode, and M.hapla, the northern root-knot nematode, in 66% and 16 % of the samples, respectively. Besides these traditional Meloidogyne species, we also detected M. chitwoodi and M. fallax, both quarantine nematodes, in field as well as in greenhouse soil samples. We suspect that these two harmful species are slowly spreading, but that few growers submit samples because they are unaware of the existence of these nematodes, or because they want to avoid official measures linked to the quarantine status. In 2011, when looking for M. chitwoodi in soil samples of fields suspected to be contaminated with this nematode, we discovered a new species for Belgium: M. artiellia, the British root-knot nematode. This species is known to cause considerable damage to rapeseed in France and to cereals, leguminous and cabbage crops in the Mediterranean region. Second-stage juveniles of Meloidogyne artiellia are relatively small and were present in low numbers (22/100ml soil), mixed with large numbers of very similar juveniles of M. naasi (180/100 ml soil). Therefore, this species can be easily missed by visual detection and its distribution might therefore be larger than reported so far. Paying attention to uncommon species, as well as observing trends in the frequency of harmful ones, are important roles of diagnostic labs. Early warnings of (potentially) harmful species can give rise to actions which prevent damage to crops, but also to international trade.