Christen D. Upper
Plant Pathology and USDA-ARS Plant Disease Resistance Research Unit
Ph.D.: University of Illinois in Chemistry

Research Program

A single acre of a crop may have more than 107 individual leaves or leaflets. Each leaf is a unique habitat. Thus, the processes that lead to the development of microbial communities on leaf surfaces are replicated a very large number of times in a single field. What forces shape the bacterial communities in these leaf-ecosystems? Bacterial population sizes may vary tremendously between apparently equivalent leaves in a plant canopy. Why? Population sizes of Pseudomonas syringae may increase 1000 fold in 24 hours following an intense rain. Why? We suspect that substrates do not limit population sizes of some bacteria on leaves. But if not nutrients, what does? Bacterial spread among leaves may occur by any of several different mechanisms. Which are the quantitatively important mechanisms that influence colonization and relative abundance of bacteria in the field?

Selected Publications

Hirano, Susan S., Amy O. Charkowski, Alan Collmer, David K. Willis, and Christen D. Upper. 1999. Role of the Hrp type III protein secretion system in growth and survival of Pseudomonas syringae pv. syringae B728a on host plants in the field. PNAS US. In press.

Hirano, S. S., Charkowski, A. O., Collmer, A., Willis, D. K., and Upper, C. D. 1998. Role(s) of pathogenicity-associated genes in interactions of populations of Pseudomonas syringae pv. syringae B728a with snap bean (Phaseolus vulgaris L.) plants in the field. Proceedings of the 7th International Congress of Plant Pathology, Edinburgh, Scotland, August 9-16, 1998.

Hirano, S. S., Willis, D. K., and Upper, C. D. 1997. Use of an intergenic region in Pseudomonas syringae pv. syringae B728a for insertion of marker cassettes for field experiments. Phytopathology 87:S42 (Abstr.).

Hirano, S. S., Ostertag, E. M., Savage, S. A., Willis, D. K., and Upper, C. D. 1997. Contribution of the regulatory gene lemA to field fitness of Pseudomonas syringae pv. syringae. Appl. Environ. Microbiol. 63:4304-4312.

Hirano, S. S., M. K. Clayton, and C. D. Upper. 1994. Estimation and temporal changes in means and variances of populations of Pseudomonas syringae on snap bean leaflets. Phytopathology 84:934-940.

Hirano, S. S. and C. D. Upper. 1993. Dynamics, spread, and persistence of a single genotype of Pseudomonas syringae relative to its conspecifics on populations of snap bean leaflets. Appl. Environ. Microbiol. 59:1082-1091.

Hudelson, B. D., M. K. Clayton, K. P. Smith, and C. D. Upper. 1992. Modeling of superimposed spatial pattern of bacterial brown spot. Phytopathology 83:430-438.

Constantinidou, H. A., S. S. Hirano, L. S. Baker, and C. D. Upper. 1990. Atmospheric dispersal of ice nucleation-active bacteria: The role of rain. Phytopathology 80:934-937.

Hirano, S. S. and C. D. Upper. 1990. Population biology and epidemiology of Pseudomonas syringae. Annu. Rev. Phytopathol. 28:155-177.

Hirano, S. S. and C. D. Upper. 1989. Diel variation in population size and ice nucleation activity of Pseudomonas syringae on snap bean leaflets. Appl. Environ. Microbiol. 55:623-630.

Back to top...