Miller, Lauren , Connolly, Brian , Beckstead, Julie .
Direct and Indirect Effects of Cheatgrass Litter on the Seed Pathogen-Cheatgrass Interaction.
The plant litter layer is an important component of seed banks that can impact seed germination and disease transmission. The invasive annual grass, cheatgrass (Bromus tectorum), has introduced large volumes of plant litter to the invaded semi-arid plant communities of the western United States. Among the plant litter of B. tectorum, a naturally-occurring fungal seed pathogen, Pyrenophora semeniperda, can be very abundant. Our goal was to determine the direct and indirect effects of B. tectorum litter on the interaction between the fungal pathogen, P. semeniperda, and B. tectorum seeds. First, we examined whether B. tectorum litter could be a direct inoculum source, infecting seeds in the seed bank. We collected B. tectorum litter in the field where P. semeniperda is present and incorporated the litter into inoculation experiments. Second, we investigated whether litter could indirectly affect the ability of the seed pathogen to infect and kill B. tectorum seeds in the seed zone, perhaps by modification of microenvironment conditions. This indirect effect was quantified by planting B. tectorum seeds into field-collected seed-zone samples from bare ground and three levels of litter depth. This experiment was repeated across years and at multiple sites. Results indicated that field-collected B. tectorum litter was not an inoculum source. Examination of indirect effects found an overall increase in pathogen-caused seed mortality with increasing litter depth. These results indicate that litter is indirectly contributing to the pathogen-seed interaction. Patterns varied across years and sites due to varying levels of natural inoculum loads. Even though litter does not directly contribute to infection, it is a very important player in determining the ability of a seed pathogen to infect seeds in the seed bank.
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1 - Gonzaga University, Department of Biology, 502 E Boone Ave, Spokane, WA, 99258, USA
2 - Washington State University, School of Biological Sciences, PO Box 644236, Pullman, WA, 99164, USA
3 - Gonzaga University, Department of Biology, 502 East Boone Avenue, Spokane, Washington, 99258, USA
Presentation Type: Poster:Posters for BSA Sections
Location: Event Tent/Cliff Lodge
Date: Tuesday, July 28th, 2009
Time: 5:30 PM