Pseudomonas corrugata , the bacteria responsible for black ( pith tomato pith necrosis ), does not seem to affect all production areas in the world. It is present on the North American continent (United States, Canada) and in several European countries (Great Britain, Netherlands, Germany, France ). Sometimes observed in the open field, it mainly affects greenhouse crops. Fairly recent work has shown that under the name “ Pseudomonas corrugata ”, two very similar bacteria are hidden for a long time: P. corrugata and P. mediterranea . The latter species was identified in France among strains believed to belong to the species P. corrugata . It has also been used in Italy, Spain, Portugal and Turkey.
 

Diseased plants see their growth blocked. Young leaves gradually chlorinate and sometimes wilt (Figures 1 and 2). Elongated, brown to black, irregularly shaped lesions are visible on the surface of the stem (Figures 2 and 4), and sometimes petioles (Figure 3). In some situations, bacterial exudates bead up on the surface of the leaflets . It should be noted that some stems become quite brittle. A longitudinal cut in the latter shows that the marrow is affected. This first takes on a translucent appearance and a pale brown tint, then gradually darkens (photo 606) ; it can also hollow out and retract to form several cavities which alternate more or less regularly with parts still intact. The T vascular derived may have a brownish color.
 

Note that in the case of black pith, the surface of the stem also undergoes other symptoms in the affected portion (s). These in fact reflect a malfunction of the plants at the origin of the emission of aerial adventitious roots (figures 4 to 7) which modifies the appearance of the stem:

- the roots can remain in the state of blanks, the stem showing more or less bumpy zones (figure 4);

- Longitudinal bursts can occur, many roots emerging from them (Figures 5 and 6);

- many roots can strew the stem over an important length (figure 7), this one also presenting a longitudinal slit.
 

It should be pointed out that if this bacteriosis can cause the total destruction of certain plants, it is also reversible: weakly affected, the plants can recover if the production conditions evolve favorably (sunny weather, therefore better light in the shelters, reduced humidity ). In some cases, the disease may even go unnoticed.
 

Let us add that a Pseudomonas fluorescens , very close to P. cichorii but different in its pathogenicity, in particular on lettuce, has been described in Canada as responsible for brownish lesions on the stem. These develop at nodes, adjacent spines and internodes. The cortex and bone marrow can also deteriorate. Unlike previous bacterial blight, the plants do not seem to wilt and dry out. This bacterium, considered to be opportunistic, is said to be rampant in the spring on plants stressed by inadequate fertilization, excessive humidity and cultivated in soil or out of soil.

For further information on this bacterium, you can consult the sheet Pseudomonas corrugata .