A Rapid Screening Method to Evaluate Maize Root Traits in the Field.

The aim of this study was to develop a scoring system for rapid phenotypic evaluation of root traits under field conditions. Phenotypic profiling was performed in 2008 and 2009 with three recombinant inbred line populations of maize (B73xMo17, OH43xW64a, NY821xH99) in a clay loam soil at the Rock Springs field station of Penn State and in a sandy soil at the Hancock field station of the University of Wisconsin. Spatial and temporal patterns in the growth angle, branching, and depth of distinct root classes were assessed visually by sampling plants at V4, flowering and physiological maturity. Root length density with depth and root elongation were quantified by soil coring and minirhizotron imaging. Excavation, preparation and evaluation of representative root crowns required about 5 minutes in the sandy soil and 10 minutes in the clay loam. Phenotypic scores by visual assessment were correlated with data from soil coring. Genotypes varied substantially for all root traits evaluated. Principle component analysis was used to condense the number of traits needed to visually assess root architecture. The scoring method permits the rapid measurement of large sets of genotypes. By means of the rapid screening method root systems tailored for improved acquisition of soil resources can be developed.