Biology and Epidemiology

- Survival and sources of inoculum

Pseudomonas cichorii survives very easily in soil and on plant debris. It colonises the rhizosphere of many cultivated crops and weeds . It infects many vegetables, such as  lettuce, cabbage, endive, celery, tomato, eggplant , flowers such as gerbera, chrysanthemum, geranium  and many weeds (figure 1) such as Sonchus oleracea, Veronica sp., Solanum nigrum, Portulaca oleracea, Poa annua, Setaria sp., Senecio vulgaris, Capsella bursa-pasteuris ...


- Penetration into the plant and invasion

Pseudomonas cichorii does not seem to have significant parasitic potential on tobacco. It mainly affects mature tobacco leaves through wounds and, perhaps via the epidermal hairs or through stomata, when the leaves are covered and saturated with water. It is present on the surface of the leaves throughout the growing period  of tobacco. Its population density fluctuates due to differences in  weather conditions and, possibly, types of tobacco.


- Dissemination of the bacteria

Bacteria dissemination occurs by water splashes, to runoffs and possibly by the seed. This is especially true on some host plants attacked by this bacterium. It can be acquired and transmitted by the leafminer Liriomyza trifolii on chrysanthemum.


- Favourable conditions for the disease development

Pseudomonas cichorii is growing at temperatures between 5 and 35 ° C, the optimum being around 20-25 ° C. Beyond 53 ° C, the bacterium cannot survive. It is particularly favoured by  moist conditions  and mature tobacco. This is why it prevails mainly during prolonged rainy periods, during which the water on the leaves is propitious for contaminations and dissemination of pathogens. It grows preferentially on dark tobacco, less vigourously on other tobacco types. Non-topped tobaccos appear to be more susceptible than topped ones.