Experimental design
In both whole plant greenhouse and in-vitro root organ culture
experiments, we employed a basic three-compartment setup
(Olsson et al.2014). One compartment contained the focal plant or root, which was then
consistently inoculated with the model strain Rhizophagus
irregularis strain A5 (Sanders Lab, hereafter A5). The second
compartment contained a second root inoculated with one of three fungal
treatments, one selfing: R. irregularis A5, and two non-selfing
fungi: R. irregularis strain B12 (Sanders Lab, hereafter
B12) or R. aggregatum (hereafter Agg), listed in order of
decreasing relatedness to the focal strain
(Roger et al. 2013).
These strains were chosen because they allowed us to test three levels
of relatedness in a genetically well-characterized genus
(Roger et al. 2013).
In both the whole plant and in-vitro setup, the roots
compartments were physically separated by a ‘fungus-only’ compartment in
which the fungi from the two hosts could directly interact (Fig. 1a&b).
To study the physical structure of fungal networks in in-vitroroot organ cultures, we covered the fungus-only compartment with a
cellophane sheet to restrict network growth to 2D top layer
(Crawford et al.1993; Hitchcock et al. 1996; Ritz et al. 1996) (Fig. 1c).
To determine the nutrient transport from the fungal network into the
host roots, we added quantum-dot tagged apatite to the partner
compartment of the in-vitro root organ cultures, and determined
how much was transferred to the focal root (Fig. 1d).