Quo vadis, breeding for an efficient root system, in the era of climate change?

Despite all the complications that arise with root research, such as slow, laborious, and unclear genetics, roots are a promising object of interest for breeders because many root traits are compatible with high yield potential. It is a great challenge for further research that there is a wide demand for information on the "hidden half of plant metabolism" from many research fields. We have summarized the main obstacles in root system research and sketched a solution for breeding in field conditions so that the result was more meaningful to the farmer. (i) The most important challenge in root research is linking the functional identification of root system properties with the aboveground parts. (ii) Field breeding is irreplaceable, and methods allowing the evaluation of roots under field conditions are indispensable. (iii) Low heritability of root system trait discourages breeders. However, root properties show broad genotypic variability, allowing the efficient use of these traits as selection criteria. (iv) The root traits are variable, and many fluctuate under the influence of environmental factors, which complicates efforts to define ideotypes and explains the different conclusions obtained by researchers from different environments. The breeding programs targeting the root system are sporadic even in a global context. This is a great reserve for breeding progress in the era of climate change, water scarcity, a possible shift to extensive farming systems, and in the era of environmental programs.