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Description of the Bacterium Causing Blight of Leek as Pseudomonas syringae pv. porri (pv. nov.)

August 1998 , Volume 88 , Number  8
Pages  844 - 850

R. Samson , H. Shafik , A. Benjama , and L. Gardan

First, second, and fourth authors: Institut National de la Recherche Agronomique, Centre d'Angers, Pathologie végétale et phytobactériologie, BP 57, 49071 Beaucouzé cedex, France; and third author: Institut National de la Recherche Agronomique, Station régionale de phytiatrie, BP 530, Marrakech, Morocco

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Accepted for publication 7 May 1998.

Forty bacterial strains isolated from leek blight (Allium porrum) in France and other countries were studied by conventional biochemical methods, serological reactions, numerical taxonomy, DNA-DNA hybridization, and ice nucleation activity, as well as by pathogenicity on leek and other host plants. They were compared with reference strains of Pseudomonas, mainly pathotype strains of P. syringae pathovars and strains of P. syringae pv. syringae isolated from various host plants including onions. Leek strains sorted with P. syringae species (sensu lato) by LOPAT tests (production of levan-sucrase, oxidase, pectinase, arginine dihydrolase, and hypersensitive reaction on tobacco). Leek strains were pathogenic to leek and produced symptoms identical to those observed in the field. They were the only strains in our study that could cause blight of leek. Thus, our results justify the creation of a new pathovar. Leek strains constituted a highly homogeneous DNA group and a discrete phenon by numerical taxonomy, and they belonged to O-serogroup POR. The name of P. syringae pv. porri is proposed for the bacterium causing leek blight. Criteria for routine identification are presented and taxonomic status is discussed.

Additional keywords: serology .

© 1998 The American Phytopathological Society