Main symptoms

White galls, gradually turning brown, more or less large and regular characterize the presence of Meloidogyne spp. ; nematodes on the roots. The nature and extent of galls depend on the species and the rate of inoculum in the soil. Those produced by Meloidogyne hapla are rather small because this nematode invades the apical meristems and therefore affects a smaller proportion of the roots, those induced by M. arenaria are the size of a pearl and affect almost all the roots. The other two major species, M. incognita and M. javanica , cause large galls sometimes covering the entire root system. Longitudinal swellings more or less tortuous and extensive are also observed.

A transverse section of the galls makes it possible to highlight the mature females, thus confirming the parasitism of these nematodes.

These root alterations disrupt the absorption of water and mineral elements, and therefore the development of plants which exhibit more or less reduced growth. The foliage can be chlorotic, and wilting sometimes occurs during the hottest hours of the day. The underside of some leaves sometimes takes on a slightly anthocyanin colouration. The lower leaves of severely affected plants show early senescence. Fruit size and yields are reduced.

In many situations, root-knot nematodes are not the only pests attacking the root system of tomatoes: they frequently contribute to predispose the roots to attacks by telluric fungi sometimes acting in complexes: Thanatephorus cucumeris (Rhizoctonia solani), Colletotrichum coccodes , Pyrenochaeta lycopersici, Sclerotium rolfsii Thus, the degradation of the roots is faster and the damage is more consequent. The Meloidogyne spp. also interact with certain tomato vascular pathogens such as Ralstonia solanacearum, Fusarium oxysporum f. sp. lycopersici and Verticillium dahliae , increasing their incidence and severity.

Conversely, the Meloidogyne-Fusarium oxysporum f. sp. lycopersici would sometimes lead to the opposite effects. Likewise, several Fusariums such as F. oxysporum and F. dimerum would lead to a reduction in the number of root galls and greater plant vigor.