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 (Al2 [SO4]3) in the laboratory, and Al2 [SO4]3 was applied at a rate of 24 mg kg−1 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.
Breeding for Al tolerance is the most sustainable strategy to reduce yield losses caused by Al toxicity in plants. The use of rapid, cheap and reliable testing methods and environments enables breeders to make quick selection decisions. The objectives of this study were to (i) identify high dry matter yielding and stable quality protein maize (QPM) lines grown under Al toxic and optimum conditions and (ii) compare the discriminating power of laboratory- and greenhouse-based testing environments. A total of 75 tropical QPM inbred lines were tested at seedling stage for dry matter yield and stability under optimum and Al toxic growing conditions across six laboratory- and greenhouse-based environments. The nutrient solution method was used for the laboratory trials, while the soil bioassay method was used for the greenhouse trials. A yield loss of 55% due to Al toxicity was observed, confirming the adverse effects of Al toxicity on maize productivity. The ANOVA revealed the presence of genetic variation among the set of genotypes used in this study, which can be exploited through plant breeding. Seventeen stable and high-yielding lines were identified and recommended. Greenhouse-based environments were more discriminating than laboratory environments. Therefore, we concluded that greenhouse environments are more informative than laboratory environments when testing genotypes for Al tolerance.
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