Pseudomonas spp.

Wet, black lesions on leaves and stems



  • Bacteria widely distributed in the world, but known to be responsible for leaf lesions mainly in Japan, Greece and Turkey.
  • Rather polyphagous, capable of infecting various plants belonging to different botanical families.
  • Can be used in the open as well as under shelter, particularly feared in cold and damp greenhouses on grafted eggplant.
  • Species associated with these leaf lesions: Pseudomonas cichorii , Pseudomonas viridiflava, Pseudomonas syringae pv. syringae , etc.
  • Organs attacked  : leaves, stems
  •  Symptoms :
    • Small dark, moist leaf spots, quickly turning brown to black, appear at the edge of the blade (Figure 1). These lesions are rather slightly angular and present a faint yellow halo (figure 2). They can spread and merge in the presence of moisture, and subsequently lead to deformation of young leaves.
    • Spots more or less extensive on leaves, initially vitreous and wet, quickly blackening, and being able to alter large sectors of the blade which end up by necrosis and drying out.
    • Extension of lesions to veins and petioles which turn brown and necrotize; severely affected leaves may turn yellow, crumble and dry out entirely.
    • Browning, blackening of more or less extensive external sectors of the stems, alteration of the pith.
    • Destruction of inflorescences, brown lesions on petioles and sepals.
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  • Signs  : no visible sign.


  • Conservation  :
    • For example Pseudomonas cichorii is very easily maintained in the soil and on plant debris. This bacterium (Figure 1) was isolated directly from soil in Japan. It colonizes the rhizosphere of a good number of hosts, cultivated or not. It is found in the pathogenic state on several vegetables, such as cabbage, endive, celery, tomato, eggplant, several legumes, tobacco, flowers (gerbera, chrysanthemum, pelargonium ...) and many weeds: Sonchus oleracea , Veronica sp., Solanum nigrum , Portulaca oleracea , Poa annua , Setaria sp., Senecio vulgaris , Capsella bursa-pasteuris ...
    • The other Pseudomonas spp. are also able to be preserved in the ground or on plant debris for several months. They also appear to be able to persist on the roots and foliage of some weeds and cultivated hosts. The seeds could make them sustainable.
  • Infection : These Pseudomonas spp. mainly penetrate the leaves through natural openings (such as stomata), or wounds (growth bursts, wounds due to wind, insect damage or related to cultivation operations, etc.). Many bacteria can be noted in the guard cells and in the intercellular spaces of the epidermis.
  • Development - Dissemination : These bacteria quickly invade leaf tissue and multiply there in very large quantities. In a few hours, thousands, then millions of bacteria are produced, especially under favorable conditions. their dispersions take place by splashing water, runoff, and during cultivation operations; workers working and circulating in crops with wet foliage contributing to their dispersal. This is particularly the case on some host plants attacked by some of these bacteria. Contaminated plants in nurseries could also contribute to their spread.
  • Favorable conditions :
    • They like temperatures that fluctuate somewhat depending on the species of Pseudomonas , in a temperature range of 5 to 35 ° C, with thermal optima being around 20 ° C.
    • Particularly appreciate the humid and sometimes cold environments of greenhouses, prolonged rainy periods during which the water deposited on the leaves is favorable to contamination and their dissemination.
    • The contribution of a strongly nitrogenous fertilizer would help to sensitize the plants,
    • Grafted plants seem more sensitive.


  • Carry out preventive crop rotations of 2 to 3 years with non-host plants.
  • Destroy the weeds because a certain number of them allow their multiplication and their maintenance in the plots.
  • Promote the  drainage of plots, avoid excess soil moisture, and monitor the sanitary quality of irrigation water.
  • Ensure a balanced manure, without excess nitrogen.
  • Avoid water stress. Do not spray, or spray them during the day, when the plants will quickly emerge.
  • Ventilate shelters as much as possible. Good crop ventilation will reduce the duration of foliage wetting and therefore prevent infections and lower the impact of these Pseudomonas spp.
  • Avoid working the plots when the foliage of the plants is still wet.
  • Avoid  leaving plant debris on the ground or burying it. If you can not do otherwise, the burial will be deep in order to activate their decomposition.
  • No protection method can very effectively control Pseudomonas spp. during cultivation.
  • Copper-based treatments in the form of salts can be used to limit the spread of these bacteriosis: copper, copper from sulphate, copper from copper hydroxide, copper from cuprous oxide, copper from oxychloride. copper. Acibenzolar-S-methyl can be used.
  • Eliminate and destroy the plants at the end of cultivation.
Last change : 10/12/21
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