بررسی اثر محلول پاشی اسید سالیسیلیک بر خصوصیات کمی و کیفی چغندر قند در سطوح مختلف آبیاری

Extended Abstract
Introduction
Sugar beet (Beta vulgaris L.) is a key sugar-producing crop in temperate regions, with global cultivation covering ~4.52 million hectares in 2023. Drought stress significantly limits its growth and yield, particularly in arid and semi-arid areas like Iran. Plants respond to water deficit through biochemical, physiological, and morphological adaptations, including altered stomatal conductance, reduced RWC, and oxidative stress. Salicylic acid, a phytohormone, modulates stress responses by enhancing antioxidant activity, photosynthetic efficiency, and osmotic regulation. This study evaluated SA’s potential to mitigate drought effects on sugar beet in Miandoab, Iran.
Materials and Methods
The experiment was conducted in a silty-loam soil (pH 7.6, EC 2.15 dS/m) using a split-plot design. Irrigation levels (normal: 60 mm, deficit: 120 mm evaporation) were assigned to main plots, and SA concentrations (0, 2, 4 mM) to subplots. The cultivar ‘Dorothy’ was sown at 100,000 plants/ha. SA was applied twice: one week before and after inducing drought. Traits measured included photosynthetic pigments, proline, RWC, stomatal conductance, root yield, sugar content, antioxidant enzymes (CAT, SOD), and MDA. Data were analyzed using SAS 9.1.
Results and Discussion:
The study investigated the effects of salicylic acid (SA) foliar application (0, 2, and 4 mM) under normal irrigation (60 mm evaporation) and water deficit (120 mm evaporation) on sugar beet physiology and yield. Water stress significantly reduced chlorophyll a (by 44.3%), chlorophyll b (by 48.7%), carotenoids (by 43.9%), relative water content (RWC, 10.1%), stomatal conductance (15.8%), and root yield (26.9%), while increasing proline (49.2%), sugar content (8.98%), and malondialdehyde (MDA, 72.4%). SA application, particularly 4 mM, mitigated these effects: under water deficit, it increased chlorophyll a (46.7%), chlorophyll b (71.3%), carotenoids (67.4%), RWC (12.1%), and stomatal conductance (14.1%), while reducing proline (12.1%) and MDA (31.1%). Antioxidant enzymes (CAT and SOD) showed elevated activity under stress, with 4 mM SA enhancing CAT by 39.2% and SOD by 146.5% compared to controls.
Yield parameters responded strongly to SA: under normal irrigation, 2 mM SA maximized root yield (97.57 t/ha) and sugar yield (15.29 t/ha), while 4 mM SA under water deficit improved root yield by 26.1% (67.12 t/ha) and sugar yield by 30.1% (12.10 t/ha) versus stressed controls. Sugar content increased by 8.98% under drought, but was highest (17.96%) with 4 mM SA. Correlation analysis revealed positive relationships between sugar yield and photosynthetic pigments (chlorophyll a: r=0.76, chlorophyll b: r=0.80), RWC (r=0.60), stomatal conductance (r=0.62), and root yield (r=0.91), but negative correlations with proline (r=-0.67) and MDA (r=-0.76).
The mechanisms of SA's protective effects involved: (1) Preservation of photosynthetic apparatus via increased chlorophyll synthesis and reduced degradation under oxidative stress, (2) Enhanced water status through improved stomatal regulation and RWC, (3) Activation of antioxidant systems (CAT, SOD) to scavenge ROS, reducing lipid peroxidation (MDA), and (4) Osmotic adjustment via moderated proline accumulation. The 4 mM SA concentration proved most effective in drought conditions, nearly equalin g normal irrigation yields, suggesting its utility for water-limited cultivation. These findings align with previous reports of SA's role in stress mitigation across crops, demonstrating its potential as a sustainable strategy for maintaining sugar beet productivity under climate-induced water scarcity.
Conclusion
This study demonstrates that foliar application of salicylic acid (SA), particularly at 4 mM, effectively mitigates drought stress in sugar beet by enhancing physiological and biochemical responses. Under water deficit, SA improved photosynthetic efficiency by preserving chlorophyll and carotenoid content, maintained leaf water status through increased RWC and stomatal conductance, and activated antioxidant enzymes (CAT, SOD) to reduce oxidative damage. These adaptations translated into significant yield improvements, with 4 mM SA increasing root yield by 26.1% and sugar yield by 30.1% compared to stressed controls. The strong positive correlations between sugar yield and photosynthetic pigments, RWC, and stomatal conductance highlight SA’s role in sustaining carbon assimilation and water-use efficiency under stress. Conversely, reduced proline and MDA levels with SA treatment confirmed its effectiveness in alleviating osmotic and oxidative stress. The results suggest that 4 mM SA can nearly compensate for yield losses under moderate drought, offering a practical strategy for sugar beet cultivation in water-limited environments. Future research should explore SA’s long-term effects and interactions with other stress-mitigation practices to optimize its field application.
Keywords: Enzyme, Photosynthetic Pigment, Physiological, Water deficit,
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