Indução de tolerância à seca em sorgo cultivado sob déficit hídrico e suplementada com silício e nitrato de potássio no pré-florescimento

Abstract

Drought as a stressful environmental agent can severely compromise the growth and production of various agricultural crops, including sorghum. However, the use of drought tolerance inducers can mitigate the effects of drought, especially silicon (Si) and potassium nitrate (KNO3). Thus, the objective of this work was to evaluate the ability of KNO3 and Si supplementation to positive modulate morphophysiological processes in order to increase the tolerance to drought of sorghum plants grown on pre-flowering water deficit. The assays to evaluate the ability of KNO3 and Si to induce drought tolerance were conducted individually under greenhouse conditions. For this, the design used for both trials was completely randomized and consisted of four treatments. To KNO3 the treatments were: field capacity (CC), water deficit (DH), field capacity + KNO3 (CC + KNO3) and water deficit + KNO3 (DH + KNO3), with six replications. Two foliar application of KNO3 at 3% (m / v) were made, the first at day zero of stress and the second at day five. The plant material used was the cultivar P898012 sensitive to drought. The Si treatments were field capacity CC, DH, CC + Si and DH + Si with six replicates. The fertigation at a concentration of 2 mM gave the silicon feed and was applied via soil in a volume of 250 ml per day for 17 days. The genotype used was BRS 331 sensitive to drought. In both experiments, the stress was imposed on preflowering and lasted for twelve days. In the dry condition, the plants treated with KNO3 presented higher levels of chlorophylls, higher photosynthetic rate, stomatal conductance, transpiration, carboxylation efficiency and higher levels of P, K, Mg, S, Cu and Fe when compared to those not treated with KNO3 . In addition, plants treated with KNO3 in this condition showed higher growth and had grain yield 32.2% higher than those that did not receive KNO3. Through these variables, it is possible to affirm that KNO3 induced drought tolerance in sorghum plants submitted to severe water stress in pre-flowering. The treatment with silicon mitigated the effects of drought on leaf potential, photosynthesis, and morphometry of the root system. Besides, it performed positively on the antioxidant system and sugar content. These positive effects contributed to a higher yield of grains and, therefore, to a greater tolerance to drought. The silicon treatment did not increase the relat ive expression of the TIP 4 aquaporins PIP1; 6 and PIP1; 3/1; 4. However, it was found in this study that aquaporin TIP 4 is more responsive to drought in sorghum plants than the aquaporins PIP1; 6 and PIP1; 3/1; 4. Therefore, it is concluded that both Si and KNO3 were effective in inducing tolerance to sorghum drought.