| Summary: | In this work, 75 quality protein maize (QPM) inbred lines were evaluated for aluminum tolerance using a nutrient solution assay in a laboratory and a soil-based technique in a greenhouse tunnel. The experiment was set up in a completely randomized design with three replications in the laboratory, and a randomized complete block design was used in the greenhouse. Aluminum toxicity was generated by amending a nutrient solution with 600 µM of aluminum sulfate (Al<sub>2</sub> [SO<sub>4</sub>]<sub>3</sub>) in the laboratory, and Al<sub>2</sub> [SO<sub>4</sub>]<sub>3</sub> was applied at a rate of 24 mg kg<sup>−1</sup> of soil in the greenhouse experiment. Relative root length (RRL) and hematoxylin staining (HS) scores were used to identify tolerant genotypes in the laboratory. According to RRL, 94.7% of genotypes were tolerant and 5.3% were sensitive, while Hematoxylin (HS) classified 77.9% of the genotypes as tolerant, and 22.1% as sensitive. RRL and HS presented a very strong negative association (−0.788). In the soil-based method, the experiments were conducted twice in successive summer seasons of 2019 and 2020. Several growth traits were measured and most genotypes that exhibited tolerance in the nutrient solution also had similar tolerance in the soil-based screening technique. Genetic variability for tolerance was identified, revealing potentially useful donors of tolerance genes in breeding programs.
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