Abnormal leaf colour

      
 
Different discolourations of the leaves are described in this section and illustrated by the photos below:
 
- Leaf mosaics (mosaic patterns and related symptoms) (figure 1);
- Yellow, chlorotic or bleached leaves (figure 2);
- Nutritional disorders;
- Chemical injuries (figures 3 and 4).

Figure 1	Figure 2	Figure 3	Figure 4

Various causes may be responsible for such symptoms :

•  either parasitic

- different viruses such as tomato spotted wilt virus (TSWV), cucumber mosaic virus (CMV), alfalfa mosaic virus (AMV), tobacco mosaic virus (TMV), potato virus Y (PVY), "ring spot" of tobacco (tobacco ring spot virus, TRSV) and other viruses (TEV, TVMV, TLCV, PVX ...);
- the Stolbur 
 

• or non-parasitic

- polyphylla (or "Frenching");
- genetic abnormalities, nutritional disorders (deficiencies or poisonings), and various chemical injuries.
 
  
Note that the diagnosis is often difficult to make. Indeed, many diseases may alter leaf colour. The abnormalities most frequently observed on the leaves are mosaics or related symptoms and yellowing. They may have different aspects depending on the disease, yet they may be quite similar for many different disorders. That is why it is difficult to identify whether the symptoms are caused by non-parasitic or parasitic diseases. We recommend you review carefully all the symptoms of this section, which is particularly well illustrated, and take your time to consider all the aspects of diagnosis. Moreover, these disorders also commonly cause alterations in leaf shape (see Abnormal leaf shape).

Figure 5	Figure 6	Figure 7

Some help models for observation are proposed in figures 5-7, do not hesitate to consult them.