Root biology and genetic improvement for drought avoidance in rice

Rice root growth encompasses a remarkable genetic diversity in terms of growth patterns, architecture, and environmental adaptations. In order to harness this valuable diversity for improving rice response to drought, an understanding of key root traits and effective drought response mechanisms is necessary. A trait-based approach with precise understanding of the target environment, including temporal and spatial heterogeneity, is a possible path toward the use of roots and dehydration avoidance traits for improved drought resistance in rice. The ability to grow deep roots is currently the most accepted target trait for improving drought resistance, but genetic variation has been reported for a number of traits that may affect drought response. Here, we review variation in rice root response to drought from a physiological perspective in terms of morphology and function with respect to the different growth environments (upland and lowland) commonly used by farmers. Recent advances in linking physiology and breeding are also presented. (C) 2011 Elsevier B.V. All rights reserved.