Control of Storage Rots on Various Pear Cultivars with a Saprophytic Strain of Pseudomonas syringae. W. J. Janisiewicz, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Appalachian Fruit Research Station, Kearneysville, WV. A. Marchi, CRIOF, University of Bologna, 20200 Bologna, Italy. Plant Dis. 76:555-560. Accepted for publication 22 January 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source, The American Phytopathological Society, 1992. DOI: 10.1094/PD-76-0555.

Dip treatment of wounded pear (Pyrus communis) fruit (cvs. Anjou, Bosc, Bartlett, and Red Bartlett) with a saprophytic strain of Pseudomonas syringae (L-59-66) provided complete or partial control of gray mold (Botrytis cinerea) and blue mold (Penicillium expansum) during storage at 18 C for 5 days or 1 C for 30 days. Cultivar, wound type, and storage temperature significantly affected the efficacy of the treatment. Control of both diseases as high as 100% was achieved in many tests with the addition of L-59-66 to a final concentration of 5.4 × 10⁸ cfu/ml in the inocula (10⁴ conidia per milliliter) of the pathogens. Disease control was best on Anjou, where frequently no rot developed, and worst on Bosc, where occasionally more than 90% of wounds developed disease. Nail wounds, which contained macerated tissue, were more difficult to protect than were clean cuts. Antagonist population in wound sites increased from 6.86 to 9.51 log cfu/ml per site during storage of fruit at 1 C for 30 days. Disease symptoms were not observed at any wound site inoculated with antagonist alone. Larger populations of antagonist were recovered from nail wounds than from cut wounds and from Bosc than from the other cultivars. Yet, the antagonist treatment was least effective with Bosc. A higher concentration of the antagonist must be used to achieve satisfactory control under these circumstances.