The epidemiology of black marrow is still poorly understood .

• Conservation, sources d'inoculum
  

Pseudomonas corrugata , a ubiquitous bacterium , is able to survive in the soil and the rhizosphere of several cultivated plants or not, whether or not they are sensitive to this pathogen of weakness. It causes symptoms of black pith on pepper and chrysanthemum and also affects Pelargonium . Artificial inoculations carried out in the stems of a few plant species have shown symptoms of black pith in eggplant, tobacco, melon, cucumber and zucchini, beans and peas, celery…. Several plants host it at the level of their root system (roots, tubers, rhizosphere) and / or their aerial vegetation (shoots, seeds), without showing symptoms: broccoli cabbage, cucumber, potato, strawberry, alfalfa, rice , tea, grapevine… P. corrugata is very present in the rhizosphere of wheat, for example.

• Penetration and invasion

This bacterium multiplies well in the rhizosphere of the tomato. It penetrates this plant through wounds present on the roots , crown and stem , and can thus begin the endophytic colonization of this nightshade. In the parasitic phase, it invades the marrow, reaches the vessels and subsequently the epidermis. Mucous bacterial exudates may form on the latter.

• Multiplication and dissemination

The bacteria present on the plants are easily disseminated by the rains and the irrigation by sprinkling , and in particular by the splashes. Dews, workers during their interventions in crops also contribute. P. corrugata can also gain, from the roots, the nutrient solution recycled from soilless crops and thus be redistributed to healthy plants. In certain situations, irrigation water would play a role in the dissemination of this bacterium.

Remember that this bacterium is transmissible by seed and that it was detected in seed lots in Israel and Egypt. The incidence of this mode of transmission is not currently known.

• Conditions favorable to its development

Depending on the country and production area, black pith manifests itself in as well as in the crops under cover open field , often in overcast and humid weather . It seems to be favored by excessive irrigation and / or nitrogen fertilization; diseased plants are often very vigorous, with extensive vegetation, large stems and succulent tissue. The disease frequently manifests itself following periods of cloudy weather and / or cold nights, in the presence of high humidity in particular under shelters. The presence of water on the leaves and the stem, as well as the wounds resulting from the leaf stripping carried out on the lower part of the stem, promote it.