Meloidogyne chitwoodi and M. fallax belong to the root-knot nematodes, which is a polyphagous group of highly adapted obligate plant pathogens of about 100 species. Root-knot nematodes are distributed world-wide and parasitise nearly every species of higher plant, where they reproduce and feed within plant roots and induce small to large galls or root-knots . Above-ground symptoms due to root-knot nematodes are not specific and often go undetected.
General symptoms include patches with poor growth of the crop, in which plants sometimes show yellowing, wilting or death of foliage, especially under draught conditions. The tuber size of infected plants can be reduced and external symptoms on the tubers, such as small pimple-like raised areas on the surface, can be found. Potential above-ground symptoms of heavily infested plants include yellowing and stunting, but even these symptoms can be absent and, if present, they are not specific for the genus Meloidogyne.Therefore, plants should be uprooted for a visual examination for the presence of galls on the roots.
Infections and gall formation may occur in geographical areas where a second nematode generation develops and where the infective juveniles hatch when new potato tubers are forming. Therefore, in the detection process, the visual observation of tuber galls may not be always reliable (in northern locations) and should be complemented with testing of asymptomatic tubers. When galls are present, their morphology can be used for identification at the genus level. Identification to the species level can only be carried out after extracting the young female from the roots. Given that species identification is very difficult by relying on morphology alone, this is not recommended. Isozymes and/or DNA methods should be used to establish the identity of the Meloidogyne species.
Meloidogyne chitwoodi and M. fallax are regulated quarantine pests in many regions and the subject of phytosanitary control.
Photo: EPPO (2024) EPPO Global Database. https://gd.eppo.int
Reference: EFSA (European Food Safety Authority), den Nijs L, Camilleri M, Diakaki M, Schenk M and Vos S 2019. Pest survey card on Meloidogyne chitwoodi and Meloidogyne fallax. EFSA supporting publication 2019: 16(2):EN-1572. 20 pp. doi:10.2903/sp.efsa.2019.EN-1572
