Evaluation of Foliar Application of Cytokinin, Iron, Zinc and Selenium on Chlorophyll Fluorescence Parameters of Wheat (Triticum aestivum L.) under Drought Stress

Document Type : Research Article

Authors

A Faridnia ¹

F Paknejad ¹

M Sadeghi Shoae ²

M. N Ilkaee ¹

F Aghayari ¹

¹ Department of Agronomy and Plant Breeding, Ka.C. Islamic Azad University, Karaj, Iran

² Sugar Beet Seed Institute (SBSI), Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran

10.22067/jcesc.2025.95050.1421

Abstract

Introduction
Environmental stresses are important factors in reducing agricultural production worldwide. Plants are continuously exposed to various stresses under natural and agricultural conditions, and water scarcity is the most important limiting factor for crop yield in most parts of the world. Drought stress can cause morphological, physiological, and biochemical changes in crop plants. Cytokinin application and foliar application of micronutrients can have beneficial effects on plant photosynthesis and wheat yield under moisture stress conditions.
Materials and Methods
This study was conducted as a split-plot factorial experiment based on a randomized complete block design with three replications in two regions, Karaj and Hamadan, during the 2019–2020 growing seasons. Irrigation regimes, including three levels—(i) irrigation at 40% available soil moisture depletion throughout the growing season (control), (ii) normal irrigation from planting to the pollination stage followed by irrigation at 60% available soil moisture depletion, and (iii) normal irrigation from planting to the pollination stage followed by irrigation cutoff until maturity—were assigned to the main plots. The factorial sub-factors included low-consumption nano-elements at five levels (control, zinc, iron, selenium, and a combined application of the three elements) and cytokinin application timing at four levels (control, flowering stage, milking stage, and flowering + milking stages). Measured traits included grain yield, biological yield, and chlorophyll fluorescence parameters.
Results and Discussion
 The results indicate that the effects of irrigation, cytokinin and Nano-micronutrient treatments on the studied traits were significant, but the interaction effects of these treatments were not significant. Drought stress has an inhibitory effect on various photosynthetic activities, especially photosystem II activity, in wheat. In the present study, it was determined that chlorophyll fluorescence parameters along with chlorophyll content have a special role in investigating the effects of drought stress on plant photosynthetic systems. Therefore, by applying drought stress, the rate of transpiration, gas exchange, maximum photochemical efficiency of photosystem II, maximum fluorescence (F_m) and photosynthesis rate decreased. However, the use of cytokinin hormone and the combined application of micronutrients significantly increased the rate of photosynthesis, stomatal conductance, transpiration intensity, maximum photochemical efficiency of photosystem II, maximum fluorescence (F_m), minimum fluorescence (F₀), relative water content of leaf and chlorophyll content. Normal irrigation treatment increased the stable fluorescence (26.68%) and the variable fluorescence index (24.78%) compared to the normal irrigation treatment until pollination and then completely stopped irrigation. Zinc + iron + selenium elements improved the stable fluorescence (26.16%) and variable fluorescence (21.48%) compared to the control treatment. Foliar application of cytokinin at pollination + grain milking increased the stable fluorescence (15.34%) and variable fluorescence (20.74%) compared to the control. Drought stress had an inhibitory effect on various activities of the photosynthetic apparatus, especially the activity of photosystem II, in wheat, but the application of micronutrients and the hormone cytokinin reduced the inhibitory effect. The improvement of photosynthesis by cytokinin and micronutrients under stress may be due to the effect of these substances in maintaining leaf chlorophyll. It seems that cytokinin and micronutrients have inhibitory effects on the functioning of the photosynthetic apparatus. According to the results obtained, it can be concluded that the decrease in the quantum yield of photosystem II is mainly due to the occurrence of disorder in the chloroplast and the decrease in chlorophyll also confirms this issue, because chlorophyll fluorescence is directly related to the activity of chlorophyll in the reaction of photosystems and can be used as a criterion for measuring the efficiency of the photosystem.
Conclusion
The combined application of nano micronutrients (zinc + iron + selenium) led to an increase in wheat yield compared to the application of each of them individually, so the combined foliar application of these three elements is recommended to increase wheat yield. Cytokinin foliar application at the pollination + grain milk stage increased wheat yield compared to application at other stages, although various sources consider the application of nano micronutrients and cytokinin foliar application important for water stress tolerance, but the results of the present study showed that in conditions of low irrigation and stress, these strategies are not recommended to reduce the negative effects of deficit irrigation.

Keywords

Chlorophyll index

Leaf relative humidity

Micronutrients

Steady fluorescence

Variable fluorescence

Subjects

• Environmental stresses

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0)

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