Bacteria Affect Plant-Mite Interactions Via Altered Scent Emissions.

Epiphytic bacteria have been shown to affect the composition of volatiles released by plants and as a consequence the behavior of other organisms towards the plant, such as herbivores and/or pathogens. In this study, we explored the effects of inoculation with three bacterial strains, namely Pseudomonas syringae, Pantoea ananatis, and Pseudomonas putida, on the composition of leaf volatile organic compounds (VOCs) emitted by bean plants (Phaseolus vulgaris L.). In addition, we examined responses of the two-spotted spider mite (Tetranychus urticae) to VOCs by measuring leaf damage and oviposition of female adults after bacterial inoculation. Colonized bean plants emitted different VOCs depending on the bacterial inoculum. The quantities of volatiles 1-undecanol and (Z)-3-hexen-1-ol significantly increased after P. syringae inoculation, while methyl salicylate and anisole increased in response to P. ananatis. T. urticae females preferred control plants over plants inoculated with P. syringae or P. putida in olfactometer assays, while no particular preference was recorded in the presence of P. ananatis. Furthermore, leaf damage caused by spider mites was 3-fold lower in plants inoculated with P. syringae than in control plants and plants inoculated with P. ananatis. Subsequently, the number of eggs laid on leaves inoculated with P. syringae was significantly lower than on those inoculated with P. ananatis or on the control ones. Moreover, a significantly higher number of spider mites selected methyl salicylate odor source over 1-undecanol, in a two-choice bioassay. The results demonstrate the bacterial involvement in plant-arthropod interactions and suggest further investigation on the potential use of bacteria as biocontrol agents in agriculture.