Early Seedling Growth as a Tool to Assess the Tolerance of Urochloa brizantha Cultivars to Free Aluminium

In this study we aimed to evaluate changes in germination, early seedling growth, and some biochemical parameters in Urochloa brizantha cultivars (Basilisk, Marandu, MG4, MG5, BRS Piatã, and Xaraés) subjected to five levels of free aluminium toxicity (0, 1, 2, 4, and 8 mmolc dm³ Al³+), and to verify the selection efficiency of aluminium tolerant cultivars. In the germination assay, lots were submitted to germination under simulated stress conditions in the laboratory, to quantify root protrusion, number of normal seedlings, shoot and root length, and dry mass. In the early seedling growth assay, evaluations were done on the seventh day after subjecting seedlings to aluminium stress conditions. Relative growth rate of length, and dry mass of shoots and roots, superoxide dismutase activity (SOD), and concentrations of proline, total antioxidants (TEAC), and malondialdehyde (MDA) were evaluated. During the seedling study period, up to 14 days after sowing, the most tolerant cultivar maintained root growth in aluminium stress conditions, while the most susceptible cultivar reduced root growth, and developed proportionally more shoots, as shoot growth depends on seed reserves. The germination assay indicated interference of the initial seed quality with increasing Al3+ concentrations. The results indicate that the early seedling growth assay, which excluded germination effects, and used the measurement of root attributes, is appropriate for the discrimination of Al3+ tolerant genotypes. The Marandu cultivar was the most similar to the Al3+ tolerance standard Basilisk cultivar.