pIAA, A Virulence Plasmid in Pseudomonas Savastanoi

Bacteria are responsible for many diseases of plants; however, only a few of the many species encountered are capable of establishing a pathogenic relationship with plants. Certain specialized functions therefore, must allow such bacteria to become pathogenic in plants. One component of pathogenicity of bacteria is expression of virulence which can be assessed on plants by the severity of the primary systems produced. Virulence, therefore, is used here as a quantitative term to describe the factor(s) responsible for production of primary symptoms in diseased plants. In the case to be discussed, the primary symptom of the disease is formation of tumorous outgrowths by the infected plant. Virulence, therefore is assessed by the size of the plant tumors incited by different strains of the pathogen. The aim of these studies is the development of concepts on virulence and its expression by the bacterium, Pseudomonas syringae p.v. savastanoi, (p. savastanoi), which causes tumors to form on oleander and olive plants. Expression of virulence is associated with genes borne on a plasmid in this bacterium.