ÍNDICES DE TOLERÂNCIA À SECA NA AVALIAÇÃO DE FORRAGEIRAS TROPICAIS

Abstract

This study aimed to evaluate the performance of Urochloa brizantha cultivars under conditions with and without water restriction using drought tolerance indices as tools to identify genotypes tolerant to water deficit. The experiment was conducted in a greenhouse using a completely randomized design in a 4×2 factorial scheme, consisting of four cultivars (Marandu, MG4, MG13 Braúna and MG5 Vitória) and two water availability levels (50% and 100% of field capacity), with six replications. Each experimental unit consisted of a plastic pot with drainage holes (8.0 dm3 capacity) containing two plants. The following variables were evaluated: plant height, number of tillers, total number of leaves, cumulative leaf length, leaf elongation rate and total dry mass yield, measured 35 days after the beginning of the treatments. The tolerance indices used were: i) Percentage Reduction (%R); ii) Stress Susceptibility Index (SSI); and iii) Stress Tolerance Index (STI). The STI proved to be the most suitable index for identifying U. brizantha cultivars with better simultaneous performance under both water deficit and optimal water conditions. The MG4 and MG13 Braúna cultivars show superior overall performance compared to MG5 Vitória and Marandu under both conditions. The Marandu cultivar exhibited greater tolerance to water stress for structural traits.