FIGURE 1.

Example of the ‘natural experiment’. Ten seeds of Populus trichocarpa from a mature capsule (from a female tree along the Clearwater River in Idaho) were opened in a laminar flow cabinet and then germinated on PDA to allow primary symbionts to emerge. In this case, six seedlings were free of culturable symbionts whereas four hosted Pseudomonas syringae, that was lethal to three of the four. In general, seedlings hosting primary symbionts can then be transplanted aseptically for inoculations with secondary symbionts, (e.g. DSE fungi, as discussed in the text) and contrasted with those free of culturable symbionts.