Impacts of Water-Stress and Proline on the Physiological, Growth, and Yield of Sunflower (Helianthus annuus L.)

Abstract

A field experiment was carried out in fields in Babylon province, Abi Gharq District, which is 10 km northwest of the center of Hilla city at longitude 44.33 degrees north and latitude 23.50 south, for the sunflower crop (Helianthus annuus L.), during the 2025-2026 growing season. To optimize water consumption in sunflower crops under water scarcity conditions and to demonstrate the effectiveness of proline acid in mitigating water stress damage due to its osmotic regulation.a randomized complete block design (RCBD) with a split-plot arrangement and three replications was used. The first factor included four water stress treatments: S₁ (50% water depletion, the control treatment), S₂, S₃, and S₄ (75%, 60%, and 45% of the water added from the control treatment, respectively), which occupied the main pot. The second factor included four levels of proline acid application: 0 (spraying with distilled water only), 30, 60, and 90 mg L⁻¹, which occupied the subpot .The study results showed that the water stress treatment S₁ was superior to treatment S₂ for most traits, including leaf area, net photosynthesis, disc diameter, fertility percentage, number of seeds per disc, and total seed yield, with averages of 4.830 and 4773 cm², 3.893 and 3.880 g m⁻² day⁻¹, 16.979 and 16.359 cm, 91.98 and 91.63%, 640.94 and 633.12 seeds, and 3.78 and 3.68 tons ha⁻¹ for the aforementioned traits and for treatments S₁ and S₂, respectively.This could save 25% of the applied water, allowing for an expansion of the cultivated area, compared to the water stress treatment S₄,which had the lowest averages for all measured traits. Similarly, the proline concentration exceeded 90 mg.L^-1. For most of the studied traits, except for net photosynthesis, fertility percentage, seed count, and total seed yield, no significant difference was observed between the concentrations of 60 and 90 mg.L^-1. This contrasts with the control treatment (spraying with distilled water), which showed a decrease in the average values ​​of all studied traits.