Fluorescent Pseudomonads Associated with Bacterial Canker of Stone Fruit in South Africa. Isabel M. M. Roos, Fruit and Fruit Technology Research Institute, Private Bag X5013, Stellenbosch 7600, South Africa. Martin J. Hattingh, Department of Plant Pathology, University of Stellenbosch, Stellenbosch 7600, South Africa. Plant Dis. 67:1267-1269. Accepted for publication 6 June 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1267.

A total of 403 oxidase-negative, green fluorescent pseudomonads were isolated from cankers, symptomless branches, and symptomless buds on plum, apricot, peach, and nectarine trees and from healthy leaves of the first two hosts. Isolates were characterized by GATTa tests for gelatin liquefaction, aesculin hydrolysis, tyrosinase activity, and tartrate utilization. Most isolates were assigned to Pseudomonas syringae pv. syringae (Pss) but P. syringae pv. morsprunorum and intermediate forms were also identified. The hypersensitive reaction on tobacco leaves was a reliable criterion for establishing pathogenicity to plum and apricot host plants. A resident phase of Pss was found on symptomless leaves and buds. Pss appeared to be the major pathogen causing bacterial canker of stone fruit in Cape Province, South Africa.

Keyword(s): epidemiology, ice nucleation, Prunus, syringomycin.