Epiphytic Populations ofPseudomonas syringaeon Susceptible and Resistant Bean Lines

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Abstract
Large differences were found in populations of virulent P. syringae (cause of bacterial brown spot of bean) on resistant and susceptible bean lines in the field. About 106 cells/g fresh wt were isolated from leaves of the susceptible ''Eagle''; compared to .apprx. 103 cells/g fresh wt from leaves of the resistant plant introduction, WBR 133. Epiphytic populations on resistant breeding lines were intermediate to those on ''Eagle'' and WBR 133. These lines were also intermediate in reaction to the brown spot pathogen. There was no direct correlation between populations of P. syringae and brown spot disease severity on the breeding lines. P. syringae was identified by morphology on Crosse''s medium and by production of typical brown spot symptoms on bean pods in 2 kinds of pod inoculation tests. Lower populations on the resistant lines apparently were not due to the presence of antagonistic epiphytic microorganisms.