|Scientific Name||Meloidogyne incognita|
|Common Names||English: Root-knot nematode; German: Wurzelgallennematode; French: Nématode des racines; Spanish: Nemátodo nódulador|
|Description||The female is pear-shaped („saccate“), about 1 mm (0.039 inch) long, with a sedentary habit, embedded in root tissues. Its pearl-white body is almost completely filled by the ovaries. It does not form a cyst. The males have an ordinary worm-like appearance.|
The physiological changes in the host plant's roots caused by larvae and adults of this nematode lead to the formation of galls („knots“). This causes a disruption of the roots' vascular system and inhibits their growth. Root elongation will often stop completely if the larvae damage the meristematic cells at the root tip. The inadequate supply of water and nutrients provided by the reduced root system causes the plant's foliage to become chlorotic or even to wilt, with an overall stunting of growth. All affected crops will produce less yield, but root crops also lose their marketability because of the distortions caused by the nematode.
In addition to the direct damage it causes, M. incognita has also been shown to increase the susceptibility of plant roots significantly to attack by bacteria and fungi - even by species they could otherwise resist - which can cause extensive secondary decay and rotting. This effect is based less on the physical damage than on the nematode's physiological effects.
The first-stage larvae remain inside their eggs. Only when they reach the second stage do they hatch and start to infest. Once a larva has bored into a root, it moves through the tissues until its head is near the vascular cylinder, preferably close to the root tip. Substances secreted in the saliva during feeding induce the formation of multinucleate giant cells and galls. This cell proliferation destroys the normal tissue structure and leads to severe dysfunction, especially if the vascular cylinder is affected and vessels become blocked or disrupted.
The nematodes pass through three further molts before reaching maturity. The adult female breaks through the epidermis and produces a gelatinous egg sac into which it deposits up to 1,000 eggs. M. incognita is parthenogenetic, so males are not necessary for reproduction. After 2-7 days, the second-stage larvae can be found in the soil. The whole life cycle lasts about a month, depending on temperature.
Additional Crop Information
M. incognita has several hundred hosts, including most cultivated crops.
M. incognita is found almost worldwide, but it prefers mild temperate areas to tropical regions. In cooler climates, it is only of importance during the warmer season and in glasshouses. It is probably the most widespread and economically important of all nematode pests, partly due to its enormous host range. It will occasionally destroy an entire crop, which has happened for instance with yams in Martinique and coffee in Brazil.
Integrated Crop Management
Soil/substrate decontamination (e.g. by steaming) prevents infestation, at least in greenhouses. Plant hygiene is important: some authors recommend warm-water treatment of seedlings as a safety measure against accidental introduction.
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