FIGURE 4.

Root system models of two rice varieties bred for contrasting agricultural systems. These root system models, generated from image series of seedling rice root systems of cv. Azucena (top), and cv. IR64 (bottom) over 10 days of growth (D1–D10) in a clear, gellan-gum nutrient media show how the breeding of crop varieties adapted to particular cultivation systems and agroecological environments has resulted in inadvertent selection for different crop root architectures. Azucena, a rice variety bred for an upland rainfed growing environment develops a deeply rooted primary and crown root architecture consistent with rapid growth in search of water, whereas IR64, bred for a water-sufficient, irrigated paddy system is more shallowly rooted, but develops longer, highly branched lateral roots in the top part of the root system to scavenge nutrient resources, such as nitrogen and phosphorus, from near the soil surface. Primary and crown roots are shown in yellow; the root system skeleton is shown in red (modified from Clark et al., 2011; models were generated using RootReader3D software).