Epiphytic Populations ofPseudomonas syringaepv.syringaeon Snap Bean and Nonhost Plants and the Incidence of Bacterial Brown Spot Disease in Relation to Cropping Patterns

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Abstract
Plots were established at 11 locations on a 64-km east-west transect through the major bean-growing area of central Wisconsin [USA]. Bacterial brown spot disease epidemics occurred in 4 of 6 plots located in the bean-growing area and in none of 5 plots outside the bean-growing area even though the bean seedlot was naturally infested with the pathogen. Epiphytic populations of P. syringae pv. syringae pathogenic to bean (Psb) were greater on symptomless bean leaflets and corn leaves from the bean-growning area than from the eastern and western portions of the transect where there was no commercial snap bean production. The pathogen was detected on hairy vetch samples from the bean-growing area only. Leaves of oak, black locust, rye and sow thistle near commercial snap bean fields supported epiphytic populations of Psb. Differences in brown spot disease incidence on beans and differences in epiphytic populations of Psb on both host and nonhost plants in different portions of the transect are probably the result of the intensive cropping of snap beans in the central part of the transect.