Aplicação foliar de 24-epibrassinolídeo na atenuação do estresse hídrico em plantas de soja nas fases de floração e enchimento dos grãos

Abstract

Soybean is one of the most important agricultural crops for world agribusiness, responsible for the production of grains, bran and soybean oil. In different cultivation environments, drought is one of the most limiting factors to the productivity of this crop. In order to reduce the negative effects of water stress, the foliar application of 24- pibrassinolide (EBL) has been used in several crops, however, studies are still scarce in oybeans in the flowering and grain filling phases. Therefore, this work aims to evaluate the efficiency of EBL on growth and physiological mechanisms in soybean in the flowering and grain filling stages under water deficit and rehydration. The experiments were carried out in a greenhouse using the cultivar IMA 84114RR. The experimental design used in both experiments was in completely randomized blocks, in a 2x2 factorial scheme (Water regimes x Application with EBL) with seven replicates. The water regimes, irrigated plants and under water stress followed by rehydration, were imposed when, in experiment I, the soybean plants were in the flowering phase and after pre-treatment with EBL, while in experiment II, the plants were in the flowering phase. grain filling. In the flowering phase, EBL promoted better recovery in plant height, number of leaves and stem diameter in relation to plants without EBL, no effect of EBL was observed for leaf area. The EBL contributed with the highest production of leaf and stem dry mass of the plants, but it did not improve soybean productivity. In irrigated plants, EBL promoted better metabolic processes such as gas exchange, photosynthesis efficiency and chlorophyll synthesis. Plants treated with EBL under water stress showed a reduction in stomatal conductance and photosynthesis similar to those without EBL. Plants with EBL showed increased transpiration and internal CO2 concentration under water stress. The maximum quantum efficiency of photosystem II (Fv/Fm) did not change in plants with and without EBL regardless of stress. Regarding the grain filling phase, the foliar application of EBL in soybean did not attenuate the gas exchanges of the stressed plants, however, it improved post-stress recovery. In addition, EBL attenuated the damage caused by water deficit on TRA and ΦPSII, which contributed to higher plant dry mass, number of pods and grains, as well as grain size.

Keywords: Glycine max. Dry. Brassinosteroids. Gas exchange. Photosystem II. Chlorophylls. Recovery.