An Overview of Bacterial Canker in Stone Fruits Caused by Different Pseudomonads: Pseudomonas syringae Species Complex and Related Species

Bacterial canker caused by different phytopathogenic pseudomonads continues to be a significant issue in stone fruit production worldwide, affecting all major fruit-growing regions. Among stone fruits, apricot and sweet and sour cherry are particularly susceptible to this disease. Over many decades, it has been consistently reported as a major problem, especially in young orchards, where infections can lead to serious economic losses, followed by tree death. Several pathogens have been identified within the Pseudomonas syringae species complex associated with stone fruits, including P. syringae pv. syringae, pv. morsprunorum (race 1 and 2), pv. persicae, pv. avii, and pv. cerasicola, as well as other pseudomonads such as Pseudomonas cerasi and P. viridiflava. Among these, pv. syringae and pv. morsprunorum are of the greatest economic importance, while pv. persicae is classified in the EU as a regulated non-quarantine pathogen. The aim of this paper is to provide an overview of the historical perspectives of bacterial canker of stone fruits, its economic importance, the taxonomic position of Pseudomonas syringae, disease symptoms, and the biology and epidemiology of the pathogens. In addition, we address bacteriological characteristics, as well as serological and molecular methods for the identification of P. syringae complex strains, and outline currently available control measures.