Table 1.
Overview of existing root phenotyping systems.
| Plant cultivation system | Growth media (localization) | Throughput | Destructive and dimensionality | Description | References |
|---|---|---|---|---|---|
| 1. X-Ray computed tomography | Soil (lab and greenhouse) | Very low (single plant at a time) | No/3D | This technique use X-ray to image root structure within a soil column. It generates stacks of projections which need to be combined and analyzed to reconstruct the 3D structure of the root system. | Mooney et al., 2011; Mairhofer et al., 2012; Mairhofer and Zappala, 2013; Koebernick et al., 2014 |
| 2. Shovelomics | Soil (field-based) | Low (Single to tens of plants in parallel, depending on available workforce) | Yes/3D | As the name imply, this method involves the manual and/or mechanical excavation of plants root systems from the soil. Roots can be measured in situ while being excavated, or phenotyped after washing and preparation. | Trachsel et al., 2011; Bucksch et al., 2014 |
| 3. Rhizotrons | Substrate (lab, field) | Low to medium (up to tens of plants in parallel) | No/2D | Rhizotrons are composed in principle of a succession of plates enclosing a thin layer of substrate. One at least of the external plates is transparent, and the rhizotron is built so that the root system grows in part or in total against this transparent plate, allowing for its imaging. In field conditions, the rhizotron can actually be a full trench along which the root system growth is observed. | Colin-Belgrand et al., 1989; Neufeld et al., 1989; Singh et al., 2010, 2012 |
| 4. Rhizolysimeters | Soil (field-based) | Low to medium (Tens to hundreds of plants in parallel) | No/3D | Rhizolysimeters are concrete, steel or PVC columns which are filled with soil and used to grow plants. The column can either be equipped with sensors or “windows” allowing for the observation and measurement of the plant as it grows by. | Eberbach and Hoffmann, 2013 |
| 5. Minirhizotron | Soil (field-based) | Low to medium (Tens to hundreds of plant in parallel) | No/3D | This particular system is based on transparent observation tubes which are permanently inserted in the soil. These tubes allow for the passage of a camera to image roots growing along the minirhizotron wall. | Iversen et al., 2012; Maeght et al., 2013 |
| 6. Growth and luminescence observatory (GLO-Roots) | Soil (lab) | Medium (tens of plants in parallel) | No/2D | Derived from the rhizotron principle, this system makes use of bioluminescent transgenic plants to image the growth of the root in soil. | Rellán-Álvarez et al., 2015 |
| 7. Rhizoscope | Liquid medium + solid support (glass beads) (lab) | High (hundreds of plants in parallel) | No/2D | This system is akin to a rhizotron. The main difference is that the growth substrate is replaced by transparent glass beads between which liquid medium is circulated. The glass beads can be removed to expose the root system for easy imaging and/or sampling. | Audebert et al., 2010 |
| 8. Clear pot method | Soil (greenhouse) | High (hundreds of plants in parallel) | No/3D | Again a variation on the rhizotron principle. Here plants are grown in transparent pots filled with soil or other potting medium. Seeds are planted close to the pot wall to enable high- throughput imaging of roots along the clear pot wall. | Richard and Hickey, 2015 |
| 9. Rhizoslides | Paper-based (lab, greenhouse) | High (hundreds of plants in parallel) | No/2D | This setup consists in growing the plants on germination paper supported by plexiglass plates and partially immerged in nutritive liquid medium, allowing for direct imaging of seedling growing on the paper. | Le Marié, 2014 |
| 10. Rhizoponics | Liquid medium (lab) | Very high (thousands of plants in parallel) | No/2D | Similar to rhizoscope systems in that it combines hydroponics and rhizotrons. The system is made of a nylon fabric supported by an aluminum frame. The set-up is immersed in a tank filled with liquid media. | Mathieu and Lobet, 2015 |
| 11. Root aeroponics | Air (lab) | Very high (thousands of plants in parallel) | No/3D | In this system plant are grown out of any kind of substrate and root are subjected to regular misting to provide water and nutrient. The root system is fully accessible at all time, albeit slumped due to growing without mechanical support. | de Dorlodot et al., 2005 |
Adapted from Paez-Garcia et al. (2015).