Changes in Assimilate Partitioning and Remobilization and Maize Water Use Efficiency under Influence of Abscisic Acid and Magnesium-Potassium Ratio under Drought Stress Conditions

Water scarcity is considered one of the major abiotic stresses that adversely affect maize growth and productivity. Although using abscisic acid, magnesium and potassium influence physiological and biochemical processes of crops to induce drought tolerance and its role in remobilization of assimilates remains unclear. This study aimed to understand the impact of exogenous application of abscisic acid and magnesium-to-potassium ratio on remobilization of assimilates and current photosynthesis for improving maize grain yield against adverse effects of drought stress. The experiment used a split-factorial randomized block design using variety (single cross 704), split by (normal irrigation, moderate drought stress severe drought stress), and was considered as the main plot. ABA 0, 50 and 100 ppm and Mg/K ratios at 0 (control), Mg/K1:1.5 (100 kg of magnesium sulfate to 150 kg of potassium sulfate) and Mg/K1:3 (100 kg of magnesium sulfate to 300 kg of potassium sulfate were considered as the factorial in the sub-plots. Results of the experiment showed that the highest amount of ABR and CDR were attributed to the moderate drought stress treatment and 50 ppm abscisic acid application, while the highest amount of CP, SPAD, number of grains per ear and grain yield belonged to the normal irrigation treatment ABA 0 ppm. Under moderate and severe drought stress conditions, the lowest CDR and CP were related to the treatment without magnesium and potassium application, while the highest CP in these two conditions was related to the application of a ratio of 100 kg magnesium sulfate to 300 kg potassium sulfate. Furthermore, the results indicated increasing consumption of potassium sulfate compared to magnesium improved grain yield by 16% and 28% compared to the control treatment under moderate and severe drought stress conditions, respectively. This finding showed magnesium should be applied in proportion to potassium at a ratio of 1 to 3 under water scarcity conditions. Therefore, moderate application of abscisic acid (50 ppm) and consumption of 300 kg of potassium sulfate combined with 100 kg of magnesium sulfate are recommended to improve maize single-cross 704 grain yield under drought stress conditions.