Somaclonal-variation-induced aluminum-sensitive mutant from an aluminum-inbred maize tolerant line

Somaclonal-variation-induced multiple mutations were observed in a progeny of the S1587 plant, regenerated from type I calli of the aluminum-tolerant inbred maize line Cat-100-6. After five generations of self-pollination, 14 progeny families of the S1587 somaclone were found to show aluminum toxicity symptoms with altered root tip morphology and reduced primary root growth. The most sensitive progeny, S1587-17, was crossed to the Cat-100-6 inbred line. The parental lines and the F1 were tested in nutrient solutions containing an aluminum activity gradient of 0-93 ⋅ 10^-6. The heterozygote behaves like the tolerant parent at aluminum activities up to 40 ⋅ 10^-6 and showed an intermediate phenotype at higher aluminum concentrations. Histological sections of aluminum-treated roots from tolerant and sensitive plants stained with hematoxylin, an aluminum marker, showed a progressive destruction of the root tip of the aluminum-sensitive genotype over time and indicated that tolerance in Cat-100-6 could be due to an aluminum exclusion mechanism. Segregation analysis of the F2 and backcross to the sensitive parent based on root morphology of plants subjected to an aluminum activity of 30 ⋅ 10^-6 showed the typical 3:1 and 1:1 tolerant:sensitive segregation ratios, respectively, indicating that tolerance in the Cat-100-6 inbred maize line is controlled by a single nuclear, semidominant gene, named Alm1.