Evaluation location: Wisconsin, United States
Ploidy determination by counting the chloroplasts contained in stomata guard cells or examining the size of the guard cells is not an exact technique for the determination of ploidy of a genotype, but does allows for the distinction of the diploid group from the other groups. Begin by collecting leaflets from the upper third of genotype to be evaluated. Place 1 or 2 drops of Iodine‐potassium iodide solution (I‐KI) in the center of a slide. With the help of fine‐point tweezers, remove the epidermal tissue from the underside of the leaf, from an area close to the veins, and immediately place it gently on the slide. Add another drop of the Iodine‐potassium iodide solution and cover with a coverslip. Examine under an optical microscope at a magnification of 100, 200 or 400X. Ploidy can be determined by looking at the size of the guard cell (L. Kramer and J. Bamberg, 2018) or via chloroplast count (Technical Manual - Potato reproductive and cytological biology - Benny Ordoñez, Matilde Orrillo and Merideth Bonierbale - 2017 International Potato Center).