The distribution of diseased plants in the crop and the location of leaf symptoms on tomato plants are essential parts of the diagnosis. Indeed, the location of the first affected plants, the speed of the spread of the disease in the crop thereafter, often inform us about the phytosanitary context and allow us to sort out biotic (parasitic, table 1) and abiotic diseases. (non-parasitic, Table 2).

In plant pathology, 5 major types of distribution of diseased plants in crops are conventionally defined. These are presented in Figure 1 and illustrated by some examples of phytosanitary contexts at the origin of these different distributions in salad plots.

Figure 1

+/-: distribution sometimes observed, especially at the start of the attack.
+: commonly observed distribution
++: distribution observed when conditions particularly favorable to the disease persist or in plots in which tomatoes have been cultivated for many years.
*: distribution observed when conditions particularly favorable to the disease persist.