Screening Corn for Al Tolerance Using Different Ca and Mg Concentrations 1

Cations such as Ca and Mg can protect roots from the toxic effects of Al. However, little use of this fact has been made in screening for Al tolerance. This study was undertaken to determine the effects of Ca and Mg concentrations in screening solutions on the toxicity of Al in roots of corn inbreds ( Zea mays L.). Two‐day‐old corn seedlings were grown for 12 days in dilute nutrient solutions containing 0.25 m M Al. Treatments consisted of Ca or Mg at concentrations of 0.5, 1.0, and 2.0 m M . The pH was adjusted to 4.60 initially with no further adjustments. The large solution: root volume ratio resulted in only small pH changes during the 12‐day screening. These small pH changes had little or no effect on the toxicity of Al in corn roots. Increasing the concentration of Ca decreased the severity of Al toxicity in roots of corn inbreds. However, there were marked differences among inbred lines in the ability of their roots to grow in these screening solutions at all levels of Ca. For example, roots of the inbred lines W153R and Va17 were susceptible and tolerant, respectively, to Al at all three levels of Ca, whereas A239 showed symptoms of severe Al toxicity at 0.5 m M and 1.0 m M Ca but produced good root growth at 2.0 m M Ca. Thus, a wide range in tolerance to Al was observed in these screening solutions by varying the concentration of Ca. At equal concentrations, Mg was as effective as Ca in protecting corn roots from Al. This technique could be utilized for screening species where a knowledge of the range in tolerance among individual genotypes is desired.