Dickeya Plant Pathogens
Résumé
Abstract
Bacteria of the genus Dickeya are phytopathogens characterised by a wide host range and large geographical distribution. The disease is named soft rot because the plant material is liquefied by bacterial enzymes. The massive production of pectate lyases is typical of Dickeya. Secretion by a specialised system named Out enables the export of pectinases that cause soft rot by cleaving pectin present in plant cell walls. The 10 species of the genus Dickeya were isolated from diseased plants or water. They attack a variety of crops and ornamental plants in tropical, subtropical and temperate climates. Dickeya solani and Dickeya dianthicola are the two main species responsible for potato diseases, leading to significant economic losses. Recent diseases on fruit trees are also due to Dickeya. These bacteria have developed different mechanisms to cope with adverse conditions and compete with other microorganisms. In addition, they use a complex regulatory network to adjust the production of pectate lyases during the successive phases of plant infection.
Key Concepts
Dickeya members are plant pathogens characterised by a broad‐host range and a large geographical distribution.
The genus Dickeya is subdivided into ten species, seven acting as phytopathogens and three found in water.
Dickeya species are ‘brute force’ pathogens as they use a set of plant cell wall degrading enzymes as their primary weapon.
Massive production of pectate lyases and accessory pectinases is the main virulence signature of the Dickeya species; they cause the symptom of rotting of the plant tissues.
Since antibiotics are not allowed in agriculture, there is currently no effective chemical control for Dickeya.
Dickeya has developed mechanisms to compete with other microorganisms and to cope with stressful conditions found in the environment or during plant colonisation.
The infectious process begins with an asymptomatic phase, corresponding to the asymptomatic presence of Dickeya in plant tissues, followed by the symptomatic phase corresponding to soft‐rot appearance.
The disease appears when environmental parameters, mainly temperatures and humidity, become favourable.
During the plant infection, the expression of pectate lyase genes is finely controlled by a complex regulatory network.
Besides pectate lyase secretion, many other functions favour the bacterial virulence, such as protein secretion systems, motility, chemotaxis, iron capture and envelope components.