Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2005
Publication Date: 9/1/2005
Citation: Barnes, C.W., Kinkel, L., Groth, J. 2005. Spatial and temporal dynamics of Puccinia andropogonis on Comandra umbellata and Andropogon gerardii in a native prairie. Canadian Journal of Botany. 83:1159-1173.
Interpretive Summary: Big bluestem (Andropogon gerardii Vitman) and comandra (Comandra umbellata L. Nutt.) are native prairie plant species that are infected by the rust Puccinia andropogonis. Big bluestem is commonly used as abundant, high-quality forage during summer, and has also been studied as one of two predominant grass species of the tall-grass prairie of North America. To complete its life cycle, P. andropogonis must infect both big bluestem and comandra. To determine the affect of distance between the two plants on disease severity of big bluestem, both plant hosts were mapped and disease severity was measured for four years. Also, a common garden was planted with a mixture of big bluestem plants representative of the study site to determine the influence of genetic variability on disease severity. The results of this study demonstrate that there is a positive relationship between disease severity on comandra and disease severity on big bluestem that decreases with increasing distance, and is limited to about 40 m. The results of this study also show that there is not a strong genetic component in big bluestem that would have influenced the relationship of distance between the two plant hosts and disease severity. This information will be used by scientists working on rust fungi life cycles as a method to control rust disease severity by manipulating plant host communities, or in research on the basic biology of naturally occurring rust fungi.
Technical Abstract: Puccinia andropogonis (Schwein.) was studied on its two hosts, comandra (Comandra umbellata L. Nutt.) and big bluestem (Andropogon gerardii Vitman) in a native prairie to investigate the influence of aecial host proximity on disease severity of the telial host in a natural system. Both hosts were mapped to measure distances from all comandra clones to selected big bluestem plants in a restored prairie in central Minnesota. Mean rust severity on big bluestem was regressed on the number of aecia on comandra (aecial density) within eight distance intervals from big bluestem plants. Distance intervals were analyzed both inclusive and exclusive of other distance intervals. There was a significant positive relationship between aecial density on comandra and rust severity on big bluestem that decreased with increasing distance in accordance with the power law model, becoming non-significant at distances > 40 m. To establish whether the genetic background of big bluestem plants influenced the relationship between rust severity and the distance to comandra, a common garden was planted with a big bluestem plant population representative of the study site. The low coefficient of determination (r2) between mean rust severities of individual plants from one year to another suggests there is not a strong genetic component in the host determining disease severity.