ABSTRACT
Demographic pressure by the growing human population is demanding increased food production, which is expanding into less favorable soils with naturally high concentration of aluminum (Al) and manganese (Mn) at pH <5.0. The emission of sulfur dioxide, ammonium, and other soil-acidifying compounds has enhanced the availability of chemical elements to wild and cultivated plants. Therefore, these soils are a major source of metal toxicity (Foy, 1988), which demands a solution. The scope for breeding crops for such soils is to reduce the transfer of aluminum and manganese to consumable plant parts. Industrial activities have created another toxicity problem: increased levels of heavy metals in soils and consequently in plants and food chains. If the metal level of these soils is to be decreased, the scope for breeding plants for such soils demands the opposite approach, i.e., enhancing the translocation of heavy metals into harvestable plant parts (Ernst, 1998b; Schat and Verkleij, 1998).
