Multicolor staining of root systems in pot culture

We have developed a method for staining the root systems of neighboring plants distinguishably in pot culture to facilitate studies of the interactions between plants. Pot soil was desiccated until the plant wilted, and then the shoot was cut and a dye solution (Fantasy) was pressure-injected into the roots at 0.05 MPa (gauge). All the roots, including fine roots of double-planted tomato (Lycopersicon esculentum var. Momotaro), in a 10-cm-diameter pot were well stained, but the root hairs were not. The volume of dye and the time required for staining were 6.4 mL and 5 h, respectively (root length 179 m plant(-1); root fresh weight 2.62 g plant(-1) on average). The root distribution of double-planted tomato in a 40 L container was well determined. The volume of dye and the time required for staining were 100 mL and 40 h, respectively (root length 1,514 m plant(-1); root dry weight 4.93 g plant(-1) on average). Each plant's roots accounted for 37-52% of the total root weight at an intermediate position between the two plants, whereas at the other positions, the roots of either plant were dominant (82-99% of total root weight). In principle, the proposed method is applicable to whole plant species with vascular systems.