Acid soil is a worldwide problemto plant production. Acid toxicity is mainly caused by a lack
of essential nutrients in the soil and excessive toxic metals in the plant root zone. Of the toxic
metals, aluminum (Al) is the most prevalent and most toxic. Plant species have evolved to
variable levels of tolerance to aluminum enabling breeding of high Al-tolerant cultivars.
Physiological and molecular approaches have revealed some mechanisms of Al toxicity in
higher plants. Mechanisms of plant tolerance to Al stress include: 1) exclusion of Al from the
root tips, and 2) absorbance, but tolerance of Al in root cells. Organic acid exudation to chelate
Al is a feature shared by many higher plants. The future challenge for Al tolerance studies is
the identification of novel tolerance mechanisms and the combination of different
mechanisms to achieve higher tolerance. Molecular approaches have led to significant
progress in explaining mechanisms and detection of genes responsible for Al tolerance.
Gene-specific molecular markers offer better options for marker-assisted selection in
breeding programs than linked marker strategies. This paper mainly focuses on recent
progress in the use of molecular approaches in Al tolerance research.