Introduction: Wheat (Triticum aestivum L.), one of the most important crops in Iran during the 2018-2019 crop year, occupied more than 5,864,000 ha of the country's agricultural lands, of which 1,932,000 ha were irrigated. Wheat cultivation in various regions of the world is impacted by a variety of abiotic stresses, among which drought stress (particularly after the pollination stage) is regarded as one of the most significant factors. In the majority of regions of Iran, there is typically sufficient moisture and suitable temperature for wheat growth in autumn and winter, but high temperatures and a lack of water are typical in spring, coinciding with wheat reproduction. Approximately 50% of the world's grain-growing lands are zinc-deficient. Considering the importance of grains in providing the daily calories required by humans, the zinc deficiency in these lands results in a zinc-deficient diet.
Materials and Methods: The present study was conducted at the Kabootarabad Agricultural Research Station in Isfahan to determine the effect of drought stress in the pollination stage, with and without zinc spraying, in the two cropping years 2017-2018 and 2018-2019. For the study, a split plot experiment with a randomized complete block design and three replications was employed. The primary factor consisted of three irrigation levels (full irrigation, and stop irrigation at the pollination stage with and without zinc foliar application), while the secondary factor was comprised of 11 wheat genotypes (two lines and 9 cultivars). In both years, the test site was chosen in areas of the station that had been fallow the year before. The land preparation process included plowing, discing, and leveling. Using a furrower, furrows with a stack distance of 60 cm were created during the final phase of land preparation. In accordance with the soil analysis, 100 kg ha^-1 of potassium fertilizer (in the form of potassium sulfate) and 100 kg ha^-1 of phosphorus fertilizer (in the form of triple superphosphate) were applied. Before planting, stemming, and before the emergence of spikes, 280 kg ha^-1 of nitrogen fertilizer (in the form of urea) was applied in equal proportions at three separate stages. This study measured the number of days to physiological maturity, the duration of the grain filling period, grain yield, number of spikes per unit area, number of seeds per spike, weight of 1,000 seeds, and zinc element efficiency. SAS were used to perform statistical analsysis, while Excel and Word were utilized to create graphs and tables. The means of the studied characteristics were statistically compared using Duncan's multi-range test at the 1% and 5% probability levels.
Results and Discussion: The interaction of stress and genotype on the number of days to physiological maturity, grain yield, and 1000-grain weight (at 1% level), as well as the effect of moisture stress on spike length at 1% level were significant. In three genotypes of Pishtaz, Backcross Roshan, and Alvand, zinc foliar application increased yield by 11.7%, 14.8%, and 15%, respectively, compared to moisture stress conditions without zinc consumption. Compared to the control treatment, the grain filling period was 33 and 30.6% shorter in the water stress treatment without zinc consumption and with zinc consumption, respectively. Among genotypes, zinc consumption efficiency ranged from 86.95% to 95.03%. This study revealed that under drought stress, foliar application of zinc can mitigate the negative effects of stress, but the response of various cultivars varies in this regard.
Conclusion: According to the findings of this study, zinc foliar spraying can enhance plant performance and mitigate unfavorable conditions caused by moisture stress. Nevertheless, genotypes react differently in this field. In this regard, genotypes such as Pishtaz, Backcross Roshan, and Alvand performed better. The increase in spike length and number of seeds per spike in response to zinc foliar application under stressful conditions were the primary causes of the yield enhancement. In drought-stressed conditions, zinc foliar application also contributed to an increase in seed yield due to a higher 1000-seed weight. Additionally, it should be noted that the effects of drought stress are closely related to ambient temperature and heat stress, and that additional experiments considering the combination of these two factors can yield more accurate results.