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Variability in Ice Nucleation Strains of Pseudomonas syringae Isolated from Diseased Woody Plants in Pacific Northwest Nurseries. S. Baca, Graduate Research Assistant, Oregon State University, Corvallis 97331. M. L. Canfield, and L. W. Moore. Research Assistant, and Associate Professor of Plant Pathology, Oregon State University, Corvallis 97331. Plant Dis. 71:412-415. Accepted for publication 13 November 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0412.

Infections incited by Pseudomonas syringae have been reported by nursery operators in many woody plants grown in Pacific Northwest nurseries. In several cases, nursery operators reported that episodes of light freezing temperatures (0 to 5 C) preceded or were associated with initial symptom development in aspen and magnolia. Because ice nucleation induced by P. syringae has been implicated as a predisposing factor to infection of other woody hosts, the association of the ice nucleation phenotype with P. syringae strains recovered from infected woody hosts was examined. Eighty-five percent or more of the strains isolated from linden, lilac, dogwood, and magnolia were ice nucleation active (INA) at 5 C; 76% of the strains from aspen were active ice nucleators, but only 30% of the strains from Japanese pear and 24% of those from red maple were active ice nucleators at 5 C. The P. syringae strains recovered from these seven woody hosts were also variable relative to the induction of a hypersensitive response in tobacco and the ability to infect green fruit of yellow pear tomato. The range in hypersensitive responses varied from 100% in aspen to 57% in Japanese pear and in pathogenicity from 100% in aspen to 36% in magnolia.

Keyword(s): frost injury.