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Pathogenicity and Numerical Analysis of Phenotypic Features of Pseudomonas syringae Strains Isolated from Deciduous Fruit Trees. Isabel M. M. Roos, Fruit and Fruit Technology Research Institute, Private Bag X5013, Stellenbosch 7600; M. J. Hattingh, Department of Plant Pathology, University of Stellenbosch, Stellenbosch 7600, South Africa. Phytopathology 77:900-908. Accepted for publication 16 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-900.

Eighty South African strains of Pseudomonas syringae and 33 reference strains were subjected to numerical phenetic analysis using 215 unit characters. Data were analyzed using unweighted pair-grouping clustering on the simple matching (Ssm) coefficient. Three phenons were distinguished at 75.8% Ssm. Most South African strains were assigned to one of two major phenons; P. s. pv. syringae (phenon 1) and race 1 of P. s. pv. morsprunorum (phenon 2). Four P. s. pv. savastanoi strains formed a tight subgroup within phenon 2. Phenon 3 comprised the reference strain of P. s. pv. morsprunorum race 2, two local race 2 strains, and a P. s. pv. papulans strain. Pathogenicity tests with five selected strains on apple, pear, plum, and cherry trees confirmed the clear distinction between the two pathovars and between races 1 and 2 of P. s. pv. morsprunorum. No significant differences in pathogenicity were detected when comparing P. s. pv. syringae strains originally isolated from a weed or from pear or nectarine trees.

Additional keywords: bacterial canker, epidemiology, host specificity.