Screening Methods for Aluminum Tolerance in Alfalfa

Reliable phenotypic assays are essential to identify genetic variation for factors limiting crop productivity. Aluminum in the soil is highly phytotoxic and is a major limitation to crop production. Current methods to evaluate Al tolerance in alfalfa (Medicago sativa L.) based on root characteristics are time consuming, labor intensive, and subject to microenvironmental variation. Our objective was to develop two rapid whole-plant assays, one in culture media and one in soil, to evaluate acid and Al tolerance in alfalfa. The culture-media method involved measuring root growth and architecture 2 wk after growing the plants in media at pH 7.0 without Al, pH 4.0 without Al, and pH 4.0 with Al. The greenhouse-based soil method is simpler, faster, and more efficient than previously used soil assays. The two assays produced similar results, consistently distinguishing between Al-sensitive and Al-tolerant alfalfa genotypes in accord with previously described assays. These whole-plant assay methods will enable the screening of breeding populations to improve Al tolerance and the dissection of the genetic determinants underlying variation in tolerance responses.