Evaluation of maize (Zea mays L.) inbred lines for tolerance to Aluminum toxicity using selection indices

Selection of genotypes with better yield performance when exposed to stress (biotic or abiotic) is key objective for every plant breeding program. Aluminum toxicity is one of the significant constraints to maize production in acidic soils in many parts of the world. The aim of this study was to identify desirable genotypes with Al tolerance based on selection indices at seedling stage and identify the most effective selection indices under Al stress conditions. 75 Quality Protein Maize (QPM) genotypes were evaluated in CRD with three replicates in the laboratory using a nutrient solution screening method. Additionally, the same genotypes were also screened in the greenhouse arranged in RCBD with three replicates using soil bioassays. The genotypes were exposed to aluminum (Al) toxicity and non-toxic conditions. Data were collected and seven selection indices namely: Stress susceptibility index (SSI); stress tolerance index (STI); geometric mean productivity (GMP); Tolerance index (TOL); Stress Resistance Index (SRI); Percentage Reduction (PCRD); and Mean Productivity (MP) were calculated. Dry Matter (DM) yield under Al toxicity and non-toxic conditions had highly significant (p < 0.001) effects with GMP, STI, SRI and MP, suggesting that these indices have the potential to differentiate genotypes for Al tolerance. Significant and negative correlations were observed between DM and PCRD, TOL, and SSI. Indices that had highly significant and very strong correlations amongst themselves were PCRD with SSI (r = 1.00), and GMP with STI (r = 1.00). The most desirable selection indices that can be used to select tolerant QPM genotypes included GMP, STI, SRI, PCRD, and TOL as they had strong correlations with dry matter under Al toxicity. The tested genotypes were classified into four groups using the principal component (PCA) analysis known as QPM genotypes with high performance under both environments (Group 1), those with high performance under optimum conditions (Group 2), genotypes with high performance under Al stress conditions (Group 3) and those with low performance under both conditions (Group 4). The top five most tolerant maize inbred lines were CML 486, QSY 2, IBL 9, IBL 5 and IBL 4. These tolerant genotypes could be used as parent material for hybridization programs in developing Al tolerant cultivars.