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Root traits contributing to plant productivity under drought

Comas, Louise H., Becker, Steven R., Cruz, Von Mark V., Byrne, Patrick F., Dierig, David A.
Frontiers in plant science 2013 v.4 pp. 1
Lesquerella, Oryza, crop production, drought, drought tolerance, geneticists, plant available water, plant breeding, plant development, plant genetics, planting, rice, root growth, root systems, roots, screening, soil depth, soil water deficit, surface water level, xylem
Geneticists and breeders are poised to breed plants with root traits that improve productivity under drought. However, they need a better understanding of root functional traits and how these traits are related to whole plant strategies to increase crop productivity under different drought conditions. Root traits associated with maintenance of plant productivity under drought include small fine root diameters, long specific root length (SRL), and great root length density, especially at depths in the soil profile where water is available. In environments with late season water deficits, small xylem diameters in targeted seminal roots save soil water deep in the soil profile for use during crop maturation and improved yields. Capacity for deep root growth and large xylem diameters in deep roots may also improve root acquisition of water when ample water at depth is available. Xylem pit anatomy that makes xylem less ‘leaky’ and prone to cavitation warrants further exploration lest such traits improve plant productivity in water limited environments without negative impacts on yields under adequate water conditions. Rapid resumption of root growth following soil rewetting may improve plant productivity under episodic drought. Genetic control of many of these traits through breeding appears feasible. Several recent reviews have covered methods for screening root traits but an appreciation for the complexity of root systems (e.g. functional differences between fine and coarse root systems) needs to be paired with these methods to successfully identify relevant traits for crop improvement. Screening of root traits at early stages in plant development can proxy traits at mature stages but verification is needed on a case by case basis that the traits are linked to increased crop productivity under drought. Examples in lesquerella (Physaria) and rice (Oryza)demonstrate phenotyping of root traits and current understanding of root trait genetics for breeding.