English name: Columbia Root-knot Nematode
Nordic names: Rodgallenematod (DK), Kolumbian juuriäkämäankeroinen (FI) Rotgallnematoder (NO), Rotgallnematoder (SE)
Major host plants
M. chitwoodi has a wide host range among several plant families, including crop plants and common weed species of both monocotyledonous and dicotyledonous. Potatoes (Solanum tuberosum) and tomatoes (Lycopersicon esculentum) are good hosts, while other crops are weak hosts. M. chitwoodi is divided into two races (race 1 and 2) which are differentiated by host specificity.
Symptoms of M. chitwoodi vary according to host, population density of the nematode and environmental conditions. Above-ground symptoms are often not obvious. On potato, pimple-like galls may or may not be produced on the tuber surface, depending on the cultivar. Galls appear as small, raised swellings on the tuber surface, giving the skin a rough appearance. Galls may be grouped in a single area of the tuber or may be scattered near the tuber eyes. Internal tissue below the gall is necrotic and brownish. Infestations are difficult to detect in freshly harvested tubers, but after a few months the egg sacs can be seen as brown spots in the cortex of cut tubers within 5–6mm of the tuber surface.
In the EPPO region it was first detected in the 1980s, in the Netherlands, but may have occurred earlier. It is possible that M. chitwoodi has a wider distribution, undetected, in Europe than is currently known.
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In the spring juveniles hatch from eggs either in the soil or attached to previously infested roots (or tubers). Larvae enter the roots (or tubers) of their host plants. Soon after entry, nematodes stimulate gall formation in the host tissue. Necrotic lesions occur in the cortex. Females are pear-shaped, whitish and remain within the root/tuber tissue, where they deposit a gelatinous egg sac from the posterior end of their body. The egg sac may contain 200 - 1000 eggs. First-stage juveniles molt within the egg to become second-stage juveniles, which emerge from the eggs about 10 days later to repeat the process, infesting other parts of the roots or developing tubers. Generation time under favourable conditions in temperate regions where potatoes are grown is typically 3-4 weeks. The nematodes overwinter as eggs, or sometimes juveniles, in infested roots, tubers, or soil.
M. chitwoodi has very limited potential for natural movement. Infected host plants or host products such as bulbs or tubers can easily transport the nematode. The movement of contaminated soil infested with M. chitwoodi could also result in spread. Infective larvae of this genus have been known to persist for more than one year in the absence of host plants. Nematode movement can also be facilitated by contaminated irrigation water.
Detection and inspection
The presence of M. chitwoodi in infested soil can be determined by sampling and extraction of the second-stage juveniles. External symptoms on tubers are obvious in the case of heavy infestations but, where nematode numbers are low or in the early stages of infection, such symptoms are not obvious. Storage of lightly infested tubers may lead to the development of obvious external symptoms.
Pest status and importance
Potato is the crop that would be most at risk from M. chitwoodi. Except from M. fallax it represents a greater threat than other Meloidogyne species already widespread in the EPPO region, in particular M. hapla, since M. chitwoodi is less easily controlled by nematicides, it has a wider host range, it produces more severe tuber symptoms and is tolerant of lower soil temperatures.
Source of information
See further information here:
Author: Christiane Scheel
Editor: Elise T. Yamamoto Buch