Plant pathogenic Pseudomonas species

In the current taxonomy, plant pathogenic Pseudomonas species are restricted to rRNA group I organisms belonging to the Gamma subclass of Proteobacteria. Currently, about 21 validly described plant pathogenic Pseudomonas species are known. The most important species is P. syringae with more than 50 described pathovars. The pathovar concept is confusing and the taxonomy of P. syringae needs revision. P. syringae pv. tomato has become an important model organism to study host reactions to pathogen infection, mainly because this pathovar can infect the model plant Arabidopsis. Plant pathogenic Pseudomonads cause important diseases on a variety of crops and symptoms include cankers, leaf and stem spots, blight, soft rot and galls. Important pathogenicity and virulence factors are the type III secretion system, ice nucleation activity, the production of secondary metabolites such as phytotoxins, pectolytic enzymes, exopolysaccharides, and hormone production. Complete genome sequences are available for three important P. syringae pathovars. Molecular methods are becoming increasingly important in the diagnosis of plant pathogenic Pseudomonas species and specific detection techniques aimed at genes involved in pathogenicity are being developed. No single control strategy is effective against the plant pathogenic Pseudomonas. Control should be based on a combination of chemical, biological and cultural strategies.