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Lack of Survival of Rhizomonas suberifaciens on Lettuce and Barley Leaves. R. Douglas O’Brien, Ken N. Jochimsen, and Ariena H. C. Van Bruggen, Department of Plant Pathology, University of California, Davis 95616. Plant Dis. 75:954-957. Accepted for publication 20 March 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0954.

Population sizes of strain CA1R of Rhizomonas suberifaciens, causal agent of corky root of lettuce, strain 714R of Pseudomonas syringae, a successful leaf colonizer, and strain EC1R of Escherichia coli, which is not a leaf epiphyte, were compared in a growth chamber. Equal densities of each strain were deposited onto lettuce (susceptible to corky root) and barley (immune to corky root) plants with an atomizer. After an initial incubation of 72 hr at 100% relative humidity, population sizes of all three strains were high, but those of P. syringae were slightly higher than those of either E. coli or R. suberifaciens. Cells of P. syringae and E. coli were more abundant on barley than on lettuce, whereas cells of R. suberifaciens were more abundant on lettuce than on barley. After a further 72-hr incubation at 50% relative humidity, populations of all strains declined, but those of P. syringae remained much larger than those of E. coli and R. suberifaciens, and those of E. coli were slightly larger than those of R. suberifaciens. Populations of R. suberifaciens, unlike those of E. coli and P. syringae, were larger on lettuce than on barley, indicating differential adaptivity of the bacteria to the two plant species. The epiphytic survival of R. suberifaciens on lettuce appears to be similar to that of E. coli, suggesting that leaves may not be a significant source of inoculum of R. suberifaciens.