Meloidogyne  spp.

Root-knot nematodes

General

• Globally widespread and extremely polyphagous, they are by far the most frequent and damaging nematodes on vegetables; their damage is sometimes considerable on farms where the management of crop rotations and the sanitary quality of the soil are not good.
• Several species of Meloidogyne are found on vegetables causing mainly root galls ( Meloidogyne incognita (Kofoid & White) Chitwood (the most widespread species), Meloidogyne arenaria (Neal) Chitwood, Meloidogyne javanic a (Treub) Chitwood and Meloidogyne hapla Chitwood (species more Nordic) Other species have been reported more occasionally: Meloidogyne chitwoodi Golden et al., Meloidogyne floridensis Handoo, Meloidogyne ethiopica Whitehaed, Meloidogyne acronea Coetzee, Meloidogyne mino r Karsen, Meloidogyne mayaguensis Rammah & Hirschmann, rather this last discovery. recently, has been described in the Americas and Africa.
• Certain isolates are able to overcome the resistance conferred in tomatoes and certain rootstocks by the “ gene Mi ” (in particular in M. incognita, M. arenaria and M. javanica ). This situation is increasingly observed in France on grafted eggplant, especially in the south-east and the south-west.
• Extremely polyphagous and attack very many plants, cultivated or not (more than 5500 plants), on which they ensure their multiplication and their conservation (pepper, eggplant, tomato, lettuce, melon, cucumber, zucchini, carrot, celery, beans, potato sweet, banana, etc.).
• Their damage is sometimes amplified by simultaneous attacks of Rhizobium radiobacter .
• Observed both in the open field and under shelters.
• Organs attacked  : roots.
• Symptoms :
  • White wales gradually turning brown, their sizes may vary depending on the species of Meloidogyne .
  • Swellings more or less tortuous and extended along the roots.
  • Leaf chlorosis and leaf wilting occurring during the hottest hours of the day.
  • Leaf and plant drying out.
  • Reduced plant development and fruit size.
  • Distribution of diseased plants in outbreaks
• >>> More pictures  
• Signs  : mature females evidenced by making a transverse cut in the galls.
• Possible confusion : rather specific root symptoms, beware of tumors caused by Rhizobium radiobacter .

Biology

• Conservation : remaining for several years in the soil in the form of egg masses protected by a mucilaginous matrix, but also thanks to a large number of host plants, whether or not cultivated, which more or less ensure their multiplication and conservation.
• Parasitism : The larvae penetrate the roots and migrate to the vessels through the cortex, between the cells. Induce galls surrounding large pear-shaped females which produce numerous eggs (300 to 3000, between 400 and 500 on average).
• Dissemination : passive of eggs and larvae by runoff, drainage and irrigation water. The larvae actively move short distances in moist soils. Dissemination is possible via soil dust, contaminated plants, tillage tools and agricultural machinery.
• Favorable conditions : active in hot and humid soils, their activity seems to be greatly reduced, or even blocked below 5 ° C and above 38 ° C. The density of soil inoculum, the influence of various stresses for plants (compacted or low humidity soil, nutritional deficiency, attacks from various pests) also influence nematode attacks and the severity of their damage.

Protection

• Perform crop rotations (soybeans, onions, garlic, corn, peanuts, Paspalum notatum, Cynodon dactylon, Eragrostis curvula, Chloris gayana, Digitaria decumbens, Panicum maximum, Crotalaria spp., Mucuna pruriens , sesame, etc.)
• Disinfect the soil by solarization or bio-disinfection .
• Immersion of infested plots for several months would help reduce soil population levels.
• Bury certain composts or green manures in the ground just before planting (coffee pulp, cake made from Azadirachta indica, Chrysanthemum coronarium, Ricinus communis, Sorghum sudanense , etc.).
• Work the soil superficially during the dry season in order to expose the nematodes to the effects of the sun.
• Thoroughly clean tools and tillage equipment from contaminated plots before use in healthy plots. Careful rinsing with water is often sufficient.
• Trap plants and / or nematicides ( Tagetes spp.), Predatory microorganisms, parasites, nematicides, plant extracts modify the development of nematodes and could be used to combat them.
• Use resistant rootstocks if they exist (mainly Solanaceae). Do not forget that losses of efficiency of resistant rootstocks are now observed due to their monocultures in certain greenhouses in particular.
• Transplanting in larger clods, this will in particular delay infestations.
• Check the sanitary quality of the plants, avoid planting contaminated ones.
• Eliminate the weeds gradually by working the soil superficially at regular intervals.
• Soak the plants during the hottest times of the day to prevent, or even reduce, wilting.
• Butter the plants to promote the development of adventitious roots.
• Eliminate the root systems of attacked plants as much as possible and destroy them in order to avoid enriching the soil with nematodes. Otherwise, the roots will be put in the open air so that they are subject to the effects of the sun.
• Composting does not completely eliminate nematodes from plant debris.
• Some nematicidal products  can be used against nematodes (consult the ANSES e-phy site ).