General Plant attacker of the month March: the root-knot nematode Meloidogyne sp.

01/03/2020
Microscoopfoto's van plantenwortels
Root with slight knot formations on the places infected with female Meloidogyne (colored pink for the image)

Meloidogyne spp. are microscopically small worms. They belong to the Nematoda or threadworms, a very diverse group of animals, a small part of which are specialized as plant parasites. Here the root-knot nematodes are the most important, because they cause great yield losses in many types of crops worldwide. About 100 species have been described. For Europe, especially M. chitwoodi and M. fallax are in the spotlight because they are becoming increasingly widespread in important crops such as potatoes and field vegetables. In addition, subtropical species such as M. incognita and M. javanica can become very problematic in Southern Europe as well as in Belgian greenhouses with fruiting vegetables. New sub-tropical species are entering Europe include M. enterolobii, M. ethiopica, M. luci.

Juvenile root-knot nematodes after hatching crawl in the soil to seek the roots of host plants. In the root they look for a suitable place where they begin to secrete certain substances that cause the plant cells to transform into a so-called giant cell. Here the nematode receives nutrients from the plant, which is weakened and therefore yields less. As a reaction, a lump or "knot" develops at the place where the nematode is living, hence the name. After several moults a female or male is formed. Females lay about 300 eggs in an egg mass that is usually deposited outside the root in the soil. Soil is an important source of spread. In potatoes, tubers are also infected by Meloidogyne sp. and the egg masses remain under the skin, an ideal way of spreading, especially in seed potatoes.

In Belgium, Meloidogyne species are occasionally detected during import controls on ornamental plants, the so-called 'phytosanitary controls'. In addition, there is a systematic control of seed potatoes for the presence of M. chitwoodi and M. fallax and, starting in 2020, there will be a survey of European fields in order to map out the distribution area even better. ILVO is working on this as a partner of the European Refereference laboratory for nematodes, by guiding all national reference laboratories in the execution of a correct diagnosis. There are also two research projects (VLAIO-Green coverings and VLAIO-Melobio) that test various control methods for Meloidogyne spp. in field crops and organic greenhouse crops.


Knobbelige aardappel
Knotty potato infested with Meloidogyne chitwoodi
Wortels
Carrot damage from Meloidogyne chitwoodi

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Nicole Viaene

Plant health and plant-pathogenic nematode expert