Environmental variation and plant disease at the interface between tallgrass prairie and agricultural systems
Though fungal and viral pathogens of tallgrass prairie plants have rarely been considered, they are common at Konza Prairie Biological Station (KPBS), an ideal setting to study the effects of environmental factors such as burning and changes in precipitation. The importance of burning for the maintenance of tallgrass prairie is clear. Burning is also used as a management tool in some commercial grass seed production systems and would be expected to destroy inoculum of pathogens in tallgrass prairie. Burning produced a substantial reduction in infection of a leaf rust fungus of the forb Erigeron strigosus in the Belowground experiment at KPBS in each year of 2000-2003. In this experiment we also observed a clear reduction in overall disease incidence during the drier years 2001-2003 compared to 2000. In a larger study of foliar pathogens (most commonly rust fungi) of 22 of dominant tallgrass prairie species in 2002-2003, the response to burning, grazing, and topographic position in KPBS watersheds varied among host species. This indicates that pathogens may contribute to more stable productivity in more diverse plant communities via different and sometimes opposing host-pathogen responses to environmental variation.
Many foliar plant pathogens such as rust fungi are known to require leaf surface moisture for successful infection. A project is underway to predict the additional effects of climate change on plant populations via changes in predicted leaf wetness duration and thus infection probabilities. In the irrigation experiment at KPBS, pathogens of the majority of plant species were present at higher incidence in the irrigated transects. There were some important exceptions, however, including leaf rusts of big bluestem and white prairie clover (Dalea candida) which showed no consistent effect of irrigation. The Dalea leaf rust has been studied over four seasons and is associated with substantial reductions in seed production and the probability of host survival. Plant gene expression in response to pathogens is sometimes similar to expression in response to drought. We have begun a project using maize microarrays to study gene regulation in the related big bluestem in response to drought stress and two common pathogens.
The complex life cycles of many of the common rust fungi at KPBS have interesting implications. We have described an Allee effect, or destabilizing density dependent reproduction, in the related fungus Tilletia indica. Many of these rust fungi probably also experience an Allee effect during sexual reproduction on their alternate host, particularly when their numbers are reduced by burning. Pathogen dependence on multiple host species probably also results in apparent competition between host species. We are in the process of modeling the likely importance of this phenomenon using published rust host profiles and the KPBS plant composition transect data. In contrast to the specialized foliar rust fungi, we have also begun a study of the population genetic structure of the common generalist soilborne pathogen Macrophomina phaseolina on native and agricultural hosts.
Host frequency-dependent effects on pathogen abundance have commonly been observed for pathogens in agricultural systems and host frequency has been manipulated as a disease management tool. The magnitude of the frequency-dependent effect may be predictable based on the life history of host and pathogen. For example, we have demonstrated in an agricultural system that the effect of host frequency is greater for a rust fungus than for the tan spot pathogen (which also infects several native grass species). At KPBS we are considering the effects of both species diversity (using plant composition transect data) and intraspecific diversity (using a new study of the population genetic structure of the dominant plant species big bluestem) on pathogen abundance. We are comparing plant species composition, big bluestem population genetic structure, and pathogen community structure in response to the watershed-level environmental treatments at KPBS.
These projects are supported by NSF,USDA, and DOE
Collaborators on these projects include:
Helen Alexander, University of Kansas
Bob Bowden, USDA-ARS, Manhattan, Kansas
Cindy Cox, The Land Institute
Shauna Dendy, Department of Plant Pathology, Kansas State University
Phil Fay, University of Minnesota
Karen Garrett, Department of Plant Pathology, Kansas State University
Sunny Power, Cornell University
Relevant Publications
In review. S. Chakraborty, J. Luck, G. Hollaway, A. Freeman, R. Norton, K. A.
Garrett, K. Percy, A. Hopkins, C. Davis, and D. F. Karnosky. Impacts
of global change on diseases of agricultural crops and forest trees.
In review. M. R. Cheatham, M. N. Rouse, P. D. Esker, S. Ignacio, W. Pradel,
R. Raymundo, A. H. Sparks, G. A. Forbes, T. R. Gordon, and K. A. Garrett.
Beyond yield: Plant disease in the context of ecosystem services.
In review. C. M. Cox, K. A. Garrett, W. W. Bockus, and L. Fang.
The response of dominant grass species in tallgrass prairie to tan spot and take-all
pathogens isolated from wheat.
In review. K. A. Garrett, S. E. Travers, G. A. Milliken, J. Bai, S. H. Hulbert, J. E. Leach, P. S. Schnable,
A. Saleh, J. L. Roe, P. A. Fay, A. K. Knapp, Z. Tang, and M. D. Smith.
Gene expression in the wild: Analyzing genome-wide expression in field experiments
with natural populations.
In review. K. A. Garrett, L. N. Zúñiga, E. Roncal, G. A. Forbes,
C. C. Mundt, Z. Su, and R. J. Nelson.
The effects of host biodiversity on disease across a climatic gradient.
In review. J. Worapong, S. P. Dendy, D. J. Awl, and K. A. Garrett.
Limiting temperatures for urediniospore germination are low in a systemic rust fungus
of tallgrass prairie.
K. A. Garrett. 2008. Climate change and plant disease risk.
In Global Climate Change and Extreme Weather Events:
Understanding the Potential Contributions to the Emergence, Reemergence and Spread of Infectious Disease.
National Academy of Science, Institute of Medicine. In revision.
K. A. Garrett and C. M. Cox. 2008.
Applied biodiversity science:
Managing emerging diseases in agriculture and linked natural systems using ecological principles.
Pages 368-386 in Infectious Disease Ecology:
Effects of Ecosystems on Disease and of Disease on Ecosystems.
R. Ostfeld, F. Keesing, and V. Eviner, editors. Princeton University Press.
[preprint PDF]
X. Han, S. P. Dendy, K. A. Garrett, L. Fang, and M. D. Smith. 2008.
Comparison of damage to native and exotic tallgrass prairie plants by natural enemies.
Plant Ecology. In press.
G. A. Milliken, K. A. Garrett, and S. E. Travers. 2007.
Experimental design for two-color microarrays applied in a pre-existing split-plot experiment.
Statistical Applications in Genetics and Molecular Biology 6, Article 20.
Available at
http://www.bepress.com/sagmb/vol6/iss1/art20[PDF]
S. E. Travers, M. D. Smith, J. Bai, S. H. Hulbert, J. E. Leach,
P. S. Schnable, A. K. Knapp,
G. Milliken, P. Fay, A. Saleh, and K. A. Garrett. 2007.
Ecological genomics: making the leap from model systems in the lab
to native populations in the field.
Frontiers in Ecology and the Environment 5:19-24.
[PDF]
K. A. Garrett, S. P. Dendy, E. E. Frank, M. N. Rouse, and S. E. Travers.
2006. Climate change effects on plant disease: Genomes to ecosystems.
Annual Review of Phytopathology 44:489-509. [PDF]
K. A. Garrett, S. H. Hulbert, J. E. Leach, and S. E. Travers. 2006.
Ecological genomics and epidemiology.
European Journal of Plant Pathology 115:35-51.
[PDF]
F. A. Al-Naimi, K. A. Garrett, and W. W. Bockus. 2005. Competition, facilitation, and niche differentiation in two foliar pathogens. Oecologia 143:449-457.
[PDF, copyright Springer]
C. M. Cox, K. A. Garrett, and W. W. Bockus. 2005. Meeting the challenge of disease management in perennial grain systems. Renewable Agriculture and Food Systems 20:15-24.
[PDF]
W. Jiang, K. A. Garrett, D. E. Peterson, T. L. Harvey, R. L. Bowden, and L. Fang.
2005. The window of risk for emigration of Wheat streak mosaic virus varies with host eradication method.
Plant Disease 89:853-858. [PDF]
C. M. Cox, K. A. Garrett, R. L. Bowden, A. K. Fritz, S. P. Dendy, and W. F. Heer. 2004. Cultivar mixtures for the simultaneous management of multiple diseases: Tan spot and leaf rust of wheat. Phytopathology 94:961-969.
[PDF]
K. A. Garrett, S. P. Dendy, A. G. Power, G. K. Blaisdell, H. A. Alexander, and J. K. McCarron.
2004. Barley yellow dwarf disease in natural populations of dominant tallgrass prairie species in Kansas [Disease Note]. Plant Disease 88:574.
[link]
K. A. Garrett and R. L. Bowden. 2002. An Allee effect reduces the invasive potential of Tilletia indica. Phytopathology 92:1152-1159.
[PDF]
K. A. Garrett and C. C. Mundt. 1999. Epidemiology in diverse host populations.
Phytopathology 89:984-990. [PDF]