A maize (Zea mays L.) field experiment conducted during the crop season 2022 at the Experimental Farm, Al-Mahnawiya, Extension Training Center, Babylon, Iraq, sought to evaluate the water stress tolerance of four maize cultivars under different irrigation regimes. The experiment used a randomized complete block design (RCBD) with a split-plot arrangement and three replications. Four irrigation treatments comprised the main plots: full irrigation (control), no irrigation during elongation (Gs-V7), no irrigation during grain-filling (Gs-R2), and no irrigation during elongation and grain-filling (Gs-V7+R2). The subplots included four maize cultivars: Furat, Dijlah, ZP, and Konsens. Leaf area decreased by 1873.76 cm² plant^-1 during the elongation stage (Gs-V7) due to non-irrigation. Non-irrigation during elongation (Gs-V7) and both elongation and grain-filling (Gs-V7+R2) reduced rows per ear, grains per row, and 500-grain weight at 11.65 and 11.02 rows ear^-1, 26.77 and 23.23 grains row^-1, and 54.90 and 63.94 g, respectively. Withholding irrigation during the elongation stage (Gs- V7), the filling (Gs-R2), and the elongation and filling phases all had decreased grain output. The lack of irrigation during the elongation stage (Gs-V7) boosted the ZmMYBE1 gene expression in vegetative phases. However, irrigation suppression did not impact the ZmMYBE1 gene expression in reproductive stages. The cultivar Furat had the most rows (17.58) and grains per row (37.58), and the cultivar Konsens had the maximum mean of 500-grain weight (84.36 g).

Keywords: Maize (Zea mays L.), irrigation regimes, cultivars, gene expression, water-stress tolerance, grain yield, yield-contributing traits

Key findings: The study demonstrated the stimulation of the ZmMYBE1 gene expression in response to water scarcity. The study also revealed significant differences among the maize cultivars based on their ability to withstand stress, as evidenced by grain yield variations and their components.