Symbioses: Plant, Animal, and Microbe Interactions
Beckstead, Julie , Meyer, Susan E. , Molder, Cherrilyn , Smith, Caitlyn .
A race for survival: Does the rate of seed germination for Bromus tectorum provide a window to escape seed death by Pyrenophora semeniperda?
THE Biotic Resistance hypothesis predicts that new enemies encountered by an introduced species will limit the species ability to establish and spread. Bromus tectorum (cheatgrass) is a successful invasive species of the Western U.S. and has encountered a new seed pathogen, Pyrenophora semeniperda. How does this invasive species cope with this new enemy? We test the hypothesis that if the germinating seed competes with the infecting fungal pathogen for seed resources stored in the endosperm, then seeds that germinate more quickly will be more likely to escape seed death in comparison to slow-germinating seeds. We found that artificial inoculations of recently harvested seeds, which germinate slowly, resulted in significantly higher mortality in comparison to levels of fast-germinating fully after-ripened seeds. Germination experiments with naturally inoculated undispersed seeds also showed that the fraction of seeds killed by the pathogen varied according to dormancy status. Disease signs were observed only on dormant seeds; fully after-ripened seeds germinated quickly and did not show disease. A third germination experiment, which manipulated secondary dormancy, utilized naturally inoculated seed bank carryover seeds stored at 2C and 20C. All three of the populations tested contained greater numbers of seeds with signs of the disease for samples stored at 2C, which germinated more slowly, in comparison to seeds stored at 20C, which had after-ripened and germinated more quickly. In support of our hypothesis, we found that the germination strategy of cheatgrass seeds can provide a window of escape from this pathogen. These results provide one mechanism by which cheatgrass is able to circumvent the negative impact of this newly encountered seed pathogen.
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1 - Gonzaga University, Department of Biology, 502 East Boone Avenue, Spokane, Washington, 99258, USA
2 - USDA Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 N 500 E, Provo, Utah, 84606, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 31st, 2006
Time: 9:00 AM