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The Relationship of Host Range, Physiology, and Genotype to Virulence on Cantaloupe in Pseudomonas syringae from Cantaloupe Blight Epidemics in France

June 2000 , Volume 90 , Number  6
Pages  636 - 646

Cindy E. Morris , Catherine Glaux , Xavier Latour , Louis Gardan , Régine Samson , and Michel Pitrat

First, second, and third authors: INRA, Pathologie Végétale, BP 94, 84143 Montfavet, France; fourth and fifth authors: INRA, Pathologie Végétale, BP 57, 49071 Beaucouzé, France; and sixth author: INRA, Génétique et Amélioration des Fruits et Légumes, BP 94, 84143 Montfavet, France

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Accepted for publication 11 February 2000.

In 1993, a bacterial blight caused important losses of cantaloupe (Cucumis melo var. cantalupensis) in southwestern France and has now been reported in 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 pathovar of the cantaloupe pathogen, we employed biochemical tests, plasmid and chromosomal profiling, and host range studies for 23 strains from cantaloupe and 47 reference strains of 14 pathovars of P. syringae. Numerical analysis of 119 traits, serological typing, syringomycin production, and BOX-polymerase chain reaction profiles did not allow us to differentiate among pathovars related to P. syringae pv. syringae. Host range studies of cantaloupe and references strains on 18 plant species showed that virulence to sugar beet was a common feature of strains virulent on cantaloupe, but was not common to strains avirulent on cantaloupe. Virulence to other species of plants varied among strains, but the overall extent of the host range was proportional to aggressiveness to cantaloupe. We propose that the strains attacking cantaloupe in France be considered P. syringae pv. aptata and that adequate host range testing may reveal that this pathovar is the cause of cantaloupe blight reported in other parts of the world.

© 2000 The American Phytopathological Society