DESCRIPTION OF THE BACTERIUM CAUSING BLIGHT OF LEEK AS PSEUDOMONAS-SYRINGAE PV. PORRI (PV. NOV.)

Forty bacterial strains isolated from leek blight (Allium porrum) in F rance and other countries were studied by conventional biochemical met hods, 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 Pseud omonas, mainly pathotype strains of P. syringae pathovars and strains of P. syringae pv. syringae isolated from various host plants includin g onions. Leek:strains sorted with P. syringae species (sensu late) by LOPAT tests (production of levan-sucrase, oxidase, pectinase, arginin e dihydrolase, and hypersensitive reaction on tobacco). Leek strains w ere pathogenic to leek and produced symptoms identical to those observ ed in the field. They were the only strains in our study that could ca use blight of leek. Thus, our results justify the creation of a new pa thovar. Leek strains constituted a highly homogeneous DNA group and a discrete phenon by numerical taxonomy, and they belonged to O-serogrou p FOR. The name of P. syringae pv. porri is proposed for the bacterium causing leek blight. Criteria for routine identification are presente d and taxonomic status is discussed.