Many diseases are at the origin of alterations and abnormalities of the roots and / or the neck that we have, for simplicity, divided into 3 general categories of symptoms exemplified below :

- Yellowing, browning, blackening of the roots (figure 4);
- Other alterations and anomalies of the roots (figure 5);
- Various alterations of the neck and of the portion of the stem close to the ground (figure 6).

 

Figure 1	Figure 2	Figure 3
Figure 4	Figure 5	Figure 6

In the presence of such symptoms, various causes are possible:

- Colletotrichum coccodes
- Didymella lycopersici
- Fusarium oxysporum f. sp. root-lycopersici
- Phytophthora spp.
- Pyrenochaeta lycopersici
- Pythium spp.
- Rhizoctonia solani ( Thanatephorus cucumeris )
- Sclerotinia sclerotiorum
- Sclerotium rolfsii ( Athelia rolsii )
- Spongospora subterranea f. sp. Mediterranean
- Meloidogyne spp. (root-knot nematodes)
- Orobanche spp.

- Root asphyxia
- Corky collar and pivot
- Various phytotoxicities

Other causes, less frequent or not encountered in France, are possible:
- des agents pathogènes : Acremomium clenched , Alternaria alternate f. sp. lycopercisi, Calyptella bell , Macrophomina phaseolina , Olpidium cabbage , Ozonium texanum ssp. parasitical , Plectosporium tabacinum , Rhizoctonia crocorum , Rhizopycnis pick , Sclerotinia minor , Thielaviopsis basicola , Agrobacterium radiobacter biovar 1, Agrobacterium tumefaciens ;
- nematodes : Globodera tabacum (cyst nematodes), Pratylenchus spp. (semi-endomigratory nematodes), and other nematodes infested with roots ( Rotylenchulus reniformis, Belonolaimus longicaudatus ...);
- abiotic causes : excess salinity, too acidic soil pH.
Additional information can be found in the work "Les maladies de la tomate" by D. Blancard, published by Éditions Quae.
 

We have deliberately grouped together the alterations of the roots, the crown and the lower part of the stem (figure 1) in the same chapter because it is not always easy to dissociate these 3 parts of plants when making a diagnosis. Indeed, the fungi attacking the roots are sometimes able to colonize the crown and the lower part of the stem. Conversely, it happens that fungi rather subservient to the crown progress towards the roots.

Identifying diseases affecting these 3 plant parts is particularly difficult as they commonly cause similar symptoms. The risks of confusion are therefore certain. We suggest that you be particularly observant and carefully follow the advice recommended throughout this chapter. If you have any doubts, contact a specialized laboratory that will be equipped to observe or isolate pests attacking the underground organs of the tomato, or located near the ground.
 

Evaluating the health status of a plant's root system is an essential act that is often poorly understood by many producers and technicians. To achieve a good diagnosis, it is advisable to place oneself in the best possible conditions of observation.

First of all, the root system (s) should be carefully recovered. For this, you will avoid tearing them brutally because the damaged parts, the most fragile (but also the most interesting for carrying out the diagnosis, will remain in the ground. Then, it will be essential to wash them well with water in order to get rid of them. particles of soil that frequently mask certain symptoms.

Once this stage of preparing the plant material has been completed, you can examine the roots (Figures 4 to 6). Do this very carefully and use a magnifying glass if you have one. This will allow you in particular to observe more closely certain structures which are all signs characterizing the presence of one or more pests. The main alterations and anomalies observed on roots are shown in figure 2.

If you observe lesions first on the neck and / or the bottom of the stem, systematically check the condition of the root system, and vice versa. Indeed, the neck may also present a certain number of lesions summarized in figure 3. In addition, we also advise you to consult the chapter External or internal alterations of the stem .

In soilless culture, observing a root system will be less of a problem although it is sometimes more difficult to recover. It will be enough to open a bag of substrate or to clear a gutter to visualize part of the roots. The health of the latter will be representative of that of the other roots buried inside the substrate. We can also consider tearing part of the “water roots” under the breads. In NFT ( cultures Nutrient Film Technic ) , the absence of substrate will facilitate observation. We will also detail the state of the collar.

The symptoms presented here are quite characteristic of a root problem, but they are not sufficient to identify the exact cause (s). They will only allow you to involve the root system in the dysfunction of the plants.