Distinção fisiológica, bioquímica, anatômica e atenuação da cavitação do algodoeiro em função da aplicação de cloreto de mepiquate sob deficiência hídrica

Abstract

Cotton (Gossypium L.) is one of the world's main agricultural commodities, and Brazil occupies a prominent position in production, consumption and export. It is a plant from arid regions, with a perennial bush characteristic that was adapted to annual non-irrigated cultivation in Brazil. To control excessive plant growth and improve the harvest rate, the use of growth regulators such as mepiquat chloride is a common practice in cotton crops. Water deficiency is one of the factors that most limit production, reducing the rate of dry matter accumulation. The occurrence of embolism is among the effects of water stress, preventing water movement in the xylem vessels. As a result, this work was carried out with the objective of analyzing physiological and anatomical responses and the vulnerability of the cotton plant to embolism in a period of water deficit of the plants that were submitted to the application of mepiquat chloride. The application of the plant regulator was performed when the average length of the 5 pointer nodes exceeded 3.5 cm. When more than 70% of the plants reached the F7 phenological stage, irrigation was suspended in order to induce water deficit. The physiological performance of the plants was evaluated through biometric analyses, carbohydrates, pigments, gas exchange and biochemical parameters (determination of O2-, H2O2 and lipid peroxidation). For the anatomical evaluation, the stomata of the adaxial and abaxial faces, leaf blade and xylem of the petiole and peduncle were analyzed. The vulnerability curves were analyzed by measuring the dissipated air along with the drop in the water potential of the plants. The experiment was established in a completely randomized design, with a 2 x 2 factorial (with deficit and without deficit x with regulator and without regulator). The results were submitted to analyzes of variance (ANAVA, p<0.05) and later the values were compared by Tukey's test (p<0.05). Those that received the application of mepiquat chloride under conditions of regular water management showed a significant increase in the dry weight of the apples. Carbohydrate content, concentration of pigments and free radicals remained unaltered in both water conditions. However, during water deficit, the gas exchanges of the plants with the regulator showed greater tolerance, maintaining their parameters for a longer time. The use of mepiquat chloride also significantly increased stomatal density during the water deficit period. The spongy parenchyma of the leaves did not show significant differences in both water regimes, but with the period of lack of water, the thickness of the cell wall of the xylem and the proportion of the xylem area in the peduncle were greater in the plants that received mepiquat chloride, presenting opposites results when analyzing the anatomy of the petiole. The vulnerability curves did not show consistent results, it is notable that there are differences between the treatments, but more tests are needed to obtain the accuracy of the curves. These results show that the use of mepiquat chloride can improve physiological, biochemical and anatomical parameters during the period of water deficit.