Aluminum (Al) toxicity is a major problem for common bean production in acid soils. The initial response of plants to Al is an inhibition of root elongation. In this study, the authors investigated the short and medium-term effects of Al treatment on root growth and Al accumulation of two common bean genotypes, VAX-1 (Al-sensitive) and Quimbaya (Al-resistant).

Both genotypes showed a severe inhibition of root elongation during the first 3-4 hours of Al treatment. However, genotype Quimbaya recovered from this inhibition, while genotype VAX-1 was increasingly damaged by Al after 12 hours of treatment.

Short-term Al treatment to different zones of the root apex showed that the transition zone (TZ) is a main target of Al. However, Al applied to the elongation zone (EZ) also contributed to the overall inhibition of root elongation.

Enhanced inhibition of root elongation during the initial 4 hours of Al treatment was related to high Al accumulation in root apices in both genotypes. However, genotype Quimbaya had lower Al contents in the root apex after 24 hours of Al treatment.

The results confirmed that genotypic differences in Al resistance in common bean are built up during medium-term exposure of the roots to Al. For this acquisition of Al resistance, the activation and maintenance of an Al exclusion mechanism, especially in the TZ but also in the EZ, appears to be decisive.

This study provides new insights into the mechanisms of Al resistance in common bean. This information could be used to develop new breeding strategies to improve Al resistance in common bean.