Root system ideotypes: what is the potential for breeding drought-tolerant grapevine rootstocks?

Adaptation to drought is one of the most important challenges for agriculture. The root system, along with its integration with the soil, is fundamental in conferring drought tolerance. At the same time, it is extremely challenging to study. The result is that investigations aimed at increasing crop drought tolerance have mainly focused on above-ground traits, especially for perennial species. In this review, we explore the root trait syndromes that would constitute drought-tolerant ideotypes, taking the example of grapevine as a model perennial grafted plant. We introduce and discuss the complexity of root trait interactions across different spatial and temporal scales considering their diversity, plasticity, and possible trade-offs. Finally, we review future approaches for discovering hidden root trait syndromes conferring drought tolerance, such as state-of-the-art root phenotyping technologies, the use of modeling as a tool to upscale root traits to the field, and new strategies to link genes to phenotypes. Together these integrated approaches can improve the breeding of drought-tolerant grapevine rootstocks.