The root knot nematode species, M. incognita, is the most widespread and probably the most serious plant parasitic nematode pest of tropical and subtropical regions throughout the world. It occurs as a pest on a very wide range of crops.
Affected plants appear in patches. Estimates of vegetable crop losses due to Meloidogyne species, mainly M. incognita and M. javanica, have ranged from 17 to 20% for aubergine (Solanum melongena), 18 to 33% for melon and 24 to 38% for tomato.
Losses of potatoes due to Meloidogyne species, mainly M. incognita, are estimated at 25% or more.
Root-knot nematodes affect a wide range of crops, particularly vegetables. M. incognita is a major economic pest of food legumes in the tropics and subtropics. Common bean (Phaseolus vulgaris) is very badly damaged by Meloidogyne species in the tropics. Cowpea (Vigna unguiculata) is another very susceptible host crop of M. incognita. Many crops grown as vegetables are susceptible to the nematode particularly tomato, aubergine, okra, cucumber, melon, carrot, gourds, lettuce and peppers. Table I shows susceptibility of various commonly grown crops to root-knot nematodes.
Table 1. Crop susceptibility to root-knot nematodes (after AfFOResT)
|Cowpea|| ||Rhodes grass|
|Gourd|| ||Sudan grass|
|Irish potato|| ||Sweet corn|
|Lettuce|| || |
|Melon|| || |
|Okra|| || |
|Parsley|| || |
|Peas|| || |
|Pumpkin|| || |
|Squash|| || |
|Sweet pepper|| || |
|Swiss chard|| || |
|Tomato|| || |
|(Source: Dobson et al. 2002)|| || |
Root-knot nematodes (Meloidogyne incognita /M. javanica) Roots of severely attacked (left) and healthy plant (right). Affected plants are normally stunted and eventually wilt and die. The most characteristic symptom is formation of root galls (knots) and these can be seen with the naked eye. Affected roots rot.
(c) A. M. Varela, icipe
Affected plants are stunted and yellow and have a tendency to wilt in hot weather. Very heavily infested plants are killed. Affected plants appear in patches. If infested plants are pulled from the soil, the roots are severely distorted, swollen and have lumps known as galls or root knots. The galls range in size from smaller than a pinhead to 25 mm or more in diameter.
Affected plant stages
Flowering stage, fruiting stage, seedling stage and vegetative growing stage.
Affected plant parts
Leaves, roots and whole plant.
Symptoms on affected plant part
Roots: galls; reduced root system; swollen roots.
Whole plant: dwarfing; wilting