Steep, Cheap, and Deep: An Ideotype for Efficient Acquisition of Water and Nitrate by Maize Root Systems.

A hypothetical integrated phenotype is presented for efficient acquisition of mobile soil resources, primarily water and nitrate, by maize root systems. The ideotype consists of shallow branched seminal roots, steep, sparsely branched nodal roots, complementary angles of crown and brace roots, nonplastic growth responses, long, dense root hairs, and several anatomical traits, including abundant root cortical aerenchyma and reduced living cortical area, that reduce the metabolic cost of soil exploration. For dense monocultures root angles should minimize interplant competition. Mulitlines of contrasting root architecture may be useful for drought-prone environments. Preliminary evidence for the adaptive value of these phenes and resulting phenotypes is available from modeling and empirical research. Significant genetic variation for these traits is present in maize germplasm.