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Direct and indirect effects of plant litter on a seed–pathogen interaction in Bromus tectorum seed banks

Published online by Cambridge University Press:  20 December 2011

Julie Beckstead ,
Lauren E. Miller  and
Brian M. Connolly
Julie Beckstead*
Affiliation:
Department of Biology, Gonzaga University, Spokane, Washington 99258, USA
Lauren E. Miller
Affiliation:
Department of Biology, Gonzaga University, Spokane, Washington 99258, USA
Brian M. Connolly
Affiliation:
Department of Biology, Gonzaga University, Spokane, Washington 99258, USA
*
*Correspondence Fax: (+1) 509-313-5804 Email: beckstead@gonzaga.edu
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Abstract

The naturally occurring fungal seed pathogen, Pyrenophora semeniperda, reduces the seed bank of Bromus tectorum but the role of plant litter in this seed–pathogen interaction is unexplored. To investigate the direct and indirect effects of litter on this interaction, we first collected field seed-bank samples from low and high Bromus litter patches. From these data, we explored the relationship between litter depth, seed-bank density and seed mortality from P. semeniperda. Second, we manipulated the fungal stages (conidial spores and mycelium) in/on the litter through sterilization techniques, to measure the direct effect of litter on seed death. Third, for indirect effects, we manipulated litter levels and held seed density and inoculum constant to determine whether Bromus litter could modify the seed zone microsites to favour disease. We found that seed-bank samples from high-litter patches contained higher field-killed seed densities compared with low-litter patches, although the percent difference of disease between litter patch types varied among sites and years (e.g. 80% to 46%). In testing the direct effects of litter on the seed–pathogen interaction, we found that litter can act as a direct inoculum source for the pathogen in the early summer but decreases in disease transmission by the following spring when the litter naturally is in contact with seeds. Investigating indirect effects, we found four times as many pathogen-killed seeds in high-litter treatments as compared with low-litter treatments when inoculum loads and seed densities were held constant. In addition, we found that litter influences the seed–pathogen interaction through density-dependent disease transmission. Our findings demonstrate the ecological importance of litter in semi-arid environments as it influences disease levels of a seed pathogen by direct and indirect means.

Keywords

cheatgrassdensity-dependent diseaseDrechslera campanulatainoculum sourcemicrobial interactionPyrenophora semeniperdashrubsteppe
Type
Research Papers
Information
Seed Science Research , Volume 22 , Issue 2 , June 2012 , pp. 135 - 144
Copyright
Copyright © Cambridge University Press 2011

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