Evolution of maize (Zea mays L.) root architectural and anatomical phenes over the past 100 years corresponds to increased tolerance of nitrogen stress


York LM, T Galindo Casta├▒eda, JR Schussler, JP Lynch


J Experimental Botany, 2015 (Cover)

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Increasing the nitrogen use efficiency of maize is an important goal for We hypothesized that through indirect selection the maize root system has evolved phenotypes suited to more intense competition for N. Sixteen maize varieties representing commercially successful lines over the past century were planted at 2 nitrogen levels and 3 planting densities. Root systems of the most recent material were 7┬║ more shallow, had 1 less nodal root per whorl, had double the distance from nodal root emergence to lateral branching, and had 14% more metaxylem vessels, but total mextaxylem vessel area remained unchanged because individual metaxylem vessels had 12% less area. We also observed plasticity in cortical phenes such as aerenchyma, which increased at greater population densities. Simulation modeling with SimRoot demonstrated that even these relatively small changes in root architecture and anatomy could increase maize shoot growth by 16% in a high density and high nitrogen environment. We conclude that evolution of maize root phenotypes over the past century is consistent with increasing nitrogen use efficiency. Introgression of more contrasting root phene states into the germplasm of elite maize and determination of the functional utility of these phene states in multiple agronomic conditions could contribute to future yield gains.