Improving tolerance to drought stress in wheat through physiological stimulation of seeds

Desert wheat’s global importance and expended cultivation in Iraq seed germination and early vigour remain highly sensitive to environmental stress, seed quality and nutrient arability limited understanding of the combine effect of gibberellins, nano zinc and Trichoderma extract, constrain strategies to enhance germination, stress tolerance and sustainable productivity. Therefor this research aims to determine the effectiveness of gibberellins, Trichoderma extract, and zinc oxide nanoparticles in increasing plant tolerance to drought stress. The study comprised two experiments; the first was a field experiment using the following treatments: seeds soaked for 12 hours in gibberellins at a concentration of 1 g/L, Trichoderma extract at a concentration of 1 ml/L, and zinc oxide nanoparticles at a concentration of 1 g/L. Four treatment replications were performed, and the seeds were sown in soil supplemented with Polyethylene Glycol (PEG) at levels of 0 and 6 g/L for two growing seasons (spring and autumn). The second experiment was a laboratory experiment using the same treatments and replications for wheat seeds. The results revealed that the grain yield reached 6.8 and 7.4 t/ha, with dry plant weights of 169.1 and 175.3 g, 1000-grain weights of 49.1 and 52.4 g, and relative growth rates of 5.1 and 6.2 g/day for plants grown in soil containing 0 and 6 grams of polyethylene glycol, respectively. The stress tolerance index was 3.444, and the accumulation rates of catalase were 4.11 and 5.28 unit/min/g, peroxidase 5.32 and 5.23 unit/min/g, carbohydrates 34.7 and 37.8 mg/g, and proline 30.1 and 33.5 µg/g in seeds treated with a mixture of gibberellins, Trichoderma extract, and zinc nanoparticles, which were grown in soil containing 0 and 6 grams of PEG, respectively, compared to the control treatment which recorded lower rates for the same traits. The results of the laboratory experiment showed that treating the seeds with a mixture of gibberellins, zinc oxide nanoparticles and Trichoderma extract led to a clear increase in the percentage of the first and final count by 98.3% for each, in feather length and dry radicle weight by 6.1 and 12.9 cm, and 5.4 and 11.0 mg respectively, and in seedling viability by 1867. This confirms the importance of adding all treatments to improve wheat's tolerance to drought, especially in the autumn.