Aluminum tolerance screening of cayenne pepper (Capsicum annuum L.) genotypes at the seedling stage under nutrient solution stress

Averaging the concentration inhibited 75% growth (IC75) is shown in the result of orthogonal polynomial regression analysis on plant height, root length, root fresh weight, root dry weight, shoot fresh weight and shoot dry weight yielded an IC75 threshold of ~1600 ppm AlCl₃·6H₂O (≈ 179 ppm Al³⁺or ≈ 6630 µM Al³⁺), which is proposed as the critical concentration for effective hydroponic screening. The (STI) analysis on the data collected from IC75 hydroponic evaluation on 41 cayenne pepper genotypes provided a robust classification into five tolerance groups, ranging from highly tolerant (HT) to highly sensitive (HS), thereby offering a clear picture of genotypic diversity in response to aluminum stress. The highly tolerant (HT) group was represented by ‘CMK Lolay’ and ‘Tanggo’, which were categorized tolerant across multiple traits. A slightly lower but still strong level of tolerance that was observed in the tolerant (T) group, they were ‘Dumay’, ‘Seulawah Aceh’, ‘Awe Aceh’, ‘Iggo’, ‘Kawat’, ‘Laris’, ‘Perintis’, ‘Landung’, and ‘PBC396’. The rest genotypes were considered as medium tolerant (MT), sensitive (S) and highly sensitive (HS). The HT and T group were potential genetic resources for breeding Al-tolerant cultivars. However, further field validation under acidic soil conditions is recommended.