Meloidogyne chitwoodi (Columbia root-knot nematode) - Fact sheet
The Columbia root-knot nematode (CRKN), Meloidogyne chitwoodi, was first described from the Pacific Northwest region of the United States in 1980. Records from Europe show that the nematode may have been present in the Netherlands as early as the 1930's. It is possible that this nematode has a wider distribution than is currently reported.
- Africa: South Africa
- Europe: Belgium, The Netherlands
- North America: Mexico (Near Mexico City), USA: California, Colorado, Idaho, New Mexico, Nevada, Oregon, Texas, Utah, Washington.
- South America: Argentina
The life cycle takes approximately 3 to 4 weeks under favourable conditions. It begins in the spring as soil temperatures rise and the second stage 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, where they become sedentary, feed and mature within the cortex. As they increase in size, they induce alteration in the cells resulting in the formation of galls from which the nematode derive their food.
The nematode undergoes 3 additional molts within the host. Worm-like males emerge from the root after the fourth molt. Females are pear-shaped, whitish when mature and remain within the root/tuber tissue, usually near the surface, where they deposit a gelatinous egg sac from the posterior end of their body. The egg sac may contain 200 to 1,000 eggs. Reproduction commonly occurs in the absence of the males through a process called mitotic parthenogenesis.
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 to 4 weeks The nematodes overwinter as eggs, or sometimes juveniles, in infested roots, tubers, or soil.
Detection and identification
Symptoms on potato
Symptoms of CRKN infection in potato tubers are highly variable and may be symptomless. Pimple-like galls may or may not be produced on the tuber surface, depending on the cultivar. When galls are produced, they appear as small, raised lumps above the developing nematodes, giving the skin a rough appearance.
Galls may be grouped in a single area or scattered near the tuber eyes. Infestations are difficult to detect in freshly harvested tubers, but after a few months the egg sacs turn from translucent to brown and can be seen as brown spots in the cortex of cut tubers. Brown spots only become evident when the females begin egg production. Internally, brown spots are usually within 5 to 6 mm of the tuber surface. There are no symptoms on potato roots and above ground symptoms are generally lacking.
Particular care needs to be exercised when examining seed potato tubers for possible root-knot nematode infection. Seed potatoes are usually produced in areas where environmental conditions may be less than ideal for root-knot nematode development and thus symptom expression. Seed potato production areas tend to have shorter growing seasons resulting in 1 to 2 generations of CRKN per year, compared to 2 or more in commercial areas, consequently, symptoms and damage on seed tubers may be lacking.
Although external symptoms of M. chitwoodi may be present, it is often difficult to detect any internal tuber damage because the females are immature and brown spots may not have developed. The best method to determine if a seed-lot is infested is to obtain soil samples from the field in question or to sample the tare soil.
Photos: Agriculture and Agri-Food Canada, Research Branch, Ottawa
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