Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/23/1996
Publication Date: N/A
Technical Abstract: To evaluate the role of hrp genes in the overall host plant-bacterial interaction, we examined the behavior of two hrp mutants, hrpZ: and hrpK, of the highly virulent strain P. syringae pv. syringae B728a (bacterial brown spot) on snap bean plants grown in the field. Loniello et al (Phytopathology 85:1148, 1995) reported that in laboratory assays, the hrpZ mutant was as virulent as the wild type when infiltrated into bean leaves but reduced in virulence when inoculated onto the surface of bean leaves. The hrpK mutant was impaired in its ability to secrete HrpZ and to cause the HR in tobacco. Mutant and wild type strains were inoculated onto bean seeds at the time of field planting. Treatments were planted in a randomized complete block design with three blocks. No significant differences have been found in the population sizes of the hrpZ mutant relative to B728a on emerging bean seedlings or leaf samples. The hrpZ mutant was isolated from brown spot lesions as was the wild type. The hrpK mutant appeared to grow on germinating seeds, but population sizes of the hrpK mutant declined on leaf samples taken from 7 to 28 DAP, indicating the mutant was substantially impaired in its ability to grow/survive on leaf habitats. Interestingly, when co- inoculated with its parent, population sizes of the hrpK mutant were larger than when it was applied alone. In summary, hrpZ in Pss B728a appears neither to be required for growth/survival, nor for disease causation on snap bean under field conditions. Growth of the hrpK mutant was slightly decreased on germinating seeds, but fitness of the bacterium was greatly diminished on bean leaf habitats in the field.