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Bacterial Ice Nucleation as a Predictor of Bacterial Brown Spot Disease on Snap Beans. S. S. Hirano, Department of Plant Pathology, USDA, University of Wisconsin, Madison 53706; D. I. Rouse(2), and C. D. Upper(3). (2)Department of Plant Pathology, USDA, University of Wisconsin, Madison 53706; (3)Agricultural Research Service, USDA, University of Wisconsin, Madison 53706. Phytopathology 77:1078-1084. Accepted for publication 26 January 1987. 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, 1987. DOI: 10.1094/Phyto-77-1078.

Snap bean plants that harbored different population sizes of Pseudomonas syringae pv. syringae were established in field plots by several combinations of seed and foliage treatments. The tube nucleation test was used to determine ice nucleation temperatures of individual bean leaflets within each of the plots at 3- or 4-day intervals throughout each of two growing seasons. The frequency with which bean leaflets harbored large population sizes of ice nucleation active P. s. pv. syringae was estimated by the frequency with which ice nucleation events occurred between 2.0 and 2.5 C. Incidence of brown spot was assessed every 3 to 4 days on the same sets of field plots. The proportion of leaflets frozen at 2.0 and 2.5 C was significantly correlated (p < 0.0001) with the incidence of brown spot assessed 38 days later. The frequency with which ice nucleation events occur on individual bean leaflets at relatively high temperatures appears to be a sufficiently reliable predictor of large pathogen populations and, therefore, of disease. The tube nucleation test shows potential for use in disease management schemes for foliar blights caused by ice nucleation active pathovars of P. syringae.