sided openings for controls and harvesting (Plate B2 in the appendix). The interior was made of black plastic to prevent light from entering the dark compartment and the exterior was covered with an aluminium sheet to prevent any heat build-up inside the chamber. Potato plantlets were fixed through small holes in the top surface. Between one-half and two thirds of the length of the stem was placed inside the dark chamber as suggested by Farran and Mingo-Castel (2006). In order to allow complete darkness, a silver stopper was rolled around the stems. Underground plant parts were periodically sprayed with the nutrient solution using six fog nozzles per chamber.
Plants were fertigated in the aeroponic system with a complete standard Steiner (1984) nutrient solution, differing in concentration at different growing stages (Table 2.1).