Rhizosphere bacterial communities associated with insect root herbivory of an invasive plant, Euphorbia esula/virgata .

Abstract

The invasive perennial plant of Eurasian origin, Euphorbia esula/virgata, has been successfully controlled over large areas in North America with a synergism between larvae of Aphthona spp. and soilborne plant pathogens. However, a multitude of sites is not yet under control. Studies are needed on how flea beetle root herbivory may alter the microbial ecology of the rhizosphere of E. esula/virgata and how the resulting rhizosphere community may affect the synergism. Studies were undertaken at Theodore Roosevelt National Park from 2001 to 2003 to identify the predominant culturable prokaryotic species found in the rhizospheres of E. esula/virgata. The hypothesis was that distinct rhizosphere communities of E. esula/virgata would be associated with root herbivory by the flea beetle Aphthona compared with rhizospheres of E. esula/virgata from stands without insect presence. Stands with and without resident populations of Aphthona spp. were assayed by spiral plating root washes of E. esula/virgata and selecting colonies from the most dilute portion of the spiral (deemed as predominant). Gas chromatographic analysis of fatty acid methyl ester was performed on the resulting pure cultures to identify the isolates and further characterize community structures using principal component analysis. Pseudomonas syringae van Hall, Pseudomonas cichorii (Swingle) Stapp, Erwinia chrysanthemii Burkholder, all plant pathogens, were associated exclusively with herbivory by Aphthona flea beetles. Conversely, Variovorax Willems et al. 1991 and Aquaspirillum Hylemon et al. 1973 spp. were a greater proportion of predominant species from roots without Aphthona present. There were also differences in the occurrence of the root pathogen antagonistic Pantoea agglomerans