Introduction: Corn is one of the most important grains, cultivated over more than 200 million hectares worldwide, with a production exceeding 1,000 million tons. Every year, global corn yields decrease by 15-20% due to drought, and this decline is expected to worsen in the coming years as drought conditions become more severe. The impact of drought stress on corn performance can vary depending on when it occurs. In tropical and subtropical regions, the estimated reduction in corn yield due to drought stress exceeds 50%. One of the primary strategies to combat drought stress is the development of stress-tolerant genotypes that utilize water efficiently. This research focuses on the impact of drought stress on the growth indicators of various corn hybrids in the region, emphasizing the importance of irrigation for summer crops amidst limited water availability during this period.



Materials and Methods: To determine the optimal moisture regime and cultivar under saline soil and water conditions, an experiment was conducted as split plots based on a randomized complete block design with four replications in 2017 at the Abbas Abad research station in Mashhad. The main factor was irrigation, comprising three moisture levels (100%, 80%, and 60% of the water requirement), while the secondary factor included different forage corn varieties (single cross hybrids 703, 704, 705, and 706). Irrigation treatments were applied once uniform greening of the field and the four-leaf stage were achieved. Watering was conducted in each plot according to the plants' water needs, using a metering system aligned with the FAO method and data from the Class A evaporation pan. To assess the physiological indicators of different treatments, six destructive samples were selected at ten-day intervals, with three plants harvested from the two middle lines of each plot. The leaf surface area was measured using a leaf meter (Delta-t), and the dry weight of the aerial parts was determined by drying the samples in an oven at 72°C for 48 hours, followed by weighing them in grams per square meter.



Results and Discussion: The analysis of variance indicated significant effects of the irrigation regime and different forage corn cultivars on the Leaf Area Index (LAI), Crop Growth Rate (CGR), and Relative Growth Rate (RGR). The changes in LAI, CGR, Net Assimilation Rate (NAR), and RGR were consistent across all hybrids, but differed among various irrigation levels. Drought stress led to a decrease in growth indices. The highest Leaf Area Index (2.6) and Crop Growth Rate (31.8 g/m²/day) were observed under the 100% water requirement treatment. Cultivar 703 exhibited the highest Crop Growth Rate (31 g/m²/day), Leaf Area Index (2.4), and Net Assimilation Rate (11.32 g/m²/day).



Conclusion: The results of this research demonstrated that water stress negatively impacted the Harvest Index, Leaf Area Index, Crop Growth Rate, Relative Growth Rate, and Net Assimilation Rate. While the trends in these indices were similar across all hybrids, they varied at different irrigation levels. Variety 703 (with a 100% water requirement) performed better than the other varieties, producing higher Leaf Area Index, Dry Matter Accumulation, and Crop Growth Rate. Therefore, ensuring 100% of the water requirement alongside cultivating single cross hybrid 703, which is more tolerant, may serve as a strategic solution for sustainable production in saline conditions.