Differences in gene expression patterns in leaves of grey poplar (Populus x canescens) under the influence of the ectomycorrhizal fungus Laccaria bicolor and the specialist leaf herbivore Chrysomela populi

The ectomycorrhizal fungus Laccaria bicolor was cultivated for three weeks in a sandwich system on a sand/peat mixture. For the controls, a sand/peat mixture without adding the fungus was prepared in the same way. Before planting, the sand/peat mixture with the fungus or without fungus was mixed with 3 l of the same sand/peat mixture as described by Müller et al. (2013). Grey poplars were grown under axenic conditions for two weeks on rooting media and directly planted in the sand/peat mixture in 3 l pots, either with or without fungal inoculum. Three weeks before the beetle bioassay the plants were placed in cages covered with mesh screen. Each cage contained L. bicolor inoculated [M] and non-inoculated [N] poplars. Ten weeks after the EMF inoculation, the NB and MB poplars were exposed to C. populi. NC and MC plants as control groups were not exposed to C. populi. For the following 14 days the beetles had the free choice between NB and MB plants. Of each plant, leaf number five from stem apex was harvested eight days after release of the beetles.