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Epiphytic Survival of Pseudomonas syringae on Hairy Vetch in Relation to Epidemiology of Bacterial Brown Spot of Bean in Wisconsin. G. L. Ercolani, Visiting Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. J. Hagedorn(2), A. Kelman(3), and R. E. Rand(4). (2)(3)(4)Professors, and Specialist, respectively, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 64:1330-1339. Accepted for publication 14 May 1974. DOI: 10.1094/Phyto-64-1330.

The bacterial brown spot pathogen, Pseudomonas syringae, highly virulent (Vi+) for bean, survived overwinter on leaves of hairy vetch in Wisconsin. Under natural conditions, these bacteria were the main components of the gram-negative epiphytic microflora on hairy vetch leaves throughout the year, except in April and from late June to mid-August. A correlation was established between the presence of high epiphytic populations of Vi+ bacteria on hairy vetch in June and subsequent outbreaks of bacterial brown spot in adjacent bean fields. High numbers of Vi+ bacteria can be spread from hairy vetch plants to bean crops during rainstorms early in the summer. Since hairy vetch is widespread as a weed in bean-growing areas in central Wisconsin, its inhabitation by Vi+ bacteria is important to the epidemiology of bacterial brown spot of bean in this region. Greenhouse studies confirmed the ability of Vi+ P. syringae to prosper as an epiphyte on hairy vetch.

Additional keywords: Epiphytic pathogen, primary inoculum source, Vicia villosa.