The relationship of host range, physiology, and genotype to virulence on cantaloupe in Pseudomonas syringae from cantaloupe blight epidemics in France

In 1993, a bacterial blight caused important losses of cantaloupe (Cucumis melo var, cantalupensis) in southwestern France and has now been reported i n all cantaloupe-growing regions of France. The causal agent of this blight is Pseudomonas syringae, although on a worldwide basis this bacterium has not been a major pathogen of melon for over 50 years. To identify the patho var of the cantaloupe pathogen, we employed biochemical tests, plasmid and chromosomal profiling, and host range studies for 23 strains from cantaloup e and 47 reference strains of 14 pathovars of P. syringae. Numerical analys is of 119 traits, serological typing, syringomycin production, and BOX-poly merase chain reaction profiles did not allow us to differentiate among path ovars related to P. syringae p. syringae. Host range studies of cantaloupe and references strains on 18 plant species showed that virulence to sugar b eet was a common feature of strains virulent on cantaloupe, but was not com mon to strains avirulent on cantaloupe. Virulence to other species of plant s varied among strains, but the overall extent of the host range was propor tional to aggressiveness to cantaloupe. We propose that the strains attacki ng cantaloupe in France be considered P. syringae P. aptata and that adequa te host range testing may reveal that this pathovar is the cause of cantalo upe blight reported in other parts of the world.