Root traits contributing to plant productivity under drought

Authors: Comas, Louise; BECKER, STEVE - Colorado State University; CRUZ, VON MARK - Colorado State University; BYRNE, PATRICK - Colorado State University; Dierig, David

Submitted to: Frontiers in Plant Science
Publication Type: Review Article
Publication Acceptance Date: 8/13/2013
Publication Date: 11/5/2013
Publication URL: https://handle.nal.usda.gov/10113/58019
Citation: Comas, L.H., Becker, S., Cruz, V.V., Byrne, P.F., Dierig, D.A. 2013. Root traits contributing to plant productivity under drought. Frontiers in Plant Science. 4:1-16. doi: 10.3389/fpls.2013.00442.

Interpretive Summary: Breeding plants with roots that more effectively take up water from soil and make it available to leaves is critical for increasing crop productivity. However, we need a better understanding of root traits and when they benefit plants. Root traits that generally benefit plants under drought stress include small root diameters, long specific root length (root length per weight), great root length density (root length per soil volume), and deep rooting (if deep soil water is available). Anatomical traits that make xylem more air tight and less prone to cavitation can also benefit plants grown with limited water without plant costs or limitations in wet conditions. Fast root growth in response to soil water may benefit plants experiencing episodic drought. Several recent reviews have covered methods for screening root traits but, to screen effectively, breeders need to understand the organization and complexity of root systems. Screening of root traits at early stages in plant development may provide information on traits at mature stages but verification is needed on a case by case basis. The genetic control of many root traits should allow breeders to breed them into plant lines.

Technical Abstract: 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. The 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 and rice demonstrate phenotyping of root traits and current genetic understanding for breeding in those crops.