Synergistic effect of indole‒3‒acetic acid and nitrogen on yield, sugar profile, and nitrogen utilization of salt-stressed sugar beet crop.

Purpose: Salt stress often reduces plant efficiency in nutrient utilization, particularly nitrogen (N), leading to physiological disorders, primarily those related to phytohormones. Hence, the current study assessed the combined effect of indole-3-acetic acid (IAA) and N in inducing salt stress tolerance in sugar beet.

Methods: Using a split-plot in randomized complete block design replicated thrice, the effect of three IAA levels (0, 150, and 300 mg L^- 1, denoted IAA₀, IAA₁₅₀ and IAA₃₀₀, respectively) and three N fertilization rates (240, 290, and 340 kg N ha^- 1, abbreviated as N₂₄₀, N₂₉₀ and N₃₄₀, respectively) on sugar beet's growth, nutritional status, and quality and sugar quality in saline soil was explored.

Results: Findings exhibited that IAA₃₀₀ × N₃₄₀ was the best combination for enhancing root diameter, leaf fresh weight, and leaf area index. Ionic homeostasis, expressed as the leaf K⁺/Na⁺ and Ca²⁺/Na⁺ ratios, reached its highest values with N₃₄₀ (1.21 and 0.51, respectively), exceeding those observed with N₂₄₀ and N₂₉₀. The IAA₀ or IAA₁₅₀ × N₃₄₀ gave the highest juice sodium content (34.0 and 33.8 mmol kg⁻¹, respectively), while N₂₄₀ across all IAA treatments recorded the lowest ones. The IAA₃₀₀ × N₃₄₀ was the most effective practice for enhancing yields and N use efficiency in sugar beet, resulting in the highest root yield (97.6 t ha⁻¹), pure sugar yield (14.50 t ha⁻¹), and N use efficiency (0.342 kg root kg⁻¹ N), significantly outperforming other IAA × N interactions.

Conclusion: In conclusion, progressive increases in IAA and N caused the enhancements sugar beet growth, yield, and related quality, since IAA at 300 mg L^- 1 plus N at 340 kg N ha^- 1 had the favorable synergism in this respect.