The influence of foliar application of cytokinin on wheat cultivars' physiological traits and yield

Wheat (Triticum aestivum L.) is one of the most important crops and is grown nearly everywhere in the world. Wheat is the primary staple food in many countries. In light of the fact that wheat yield varies depending on environmental conditions, it is crucial to employ strategies that increase wheat yield. To investigate the effects of foliar application of cytokinin on the physiological traits and yield of wheat cultivars, a factorial experiment based on randomized complete block design with tree replications was conducted at the research farm of the Agriculture Faculty, University of Zanjan, during the 2016 cropping seasons. Six wheat cultivars (Azadi, Karaj 3, Roshan, Falat, Sardari and Yavarus) were treated with foliar applications of cytokinin (6-benzylaminopurine) at two levels (0 (control) and 50 µM). At the 50% stage of cluster emergence (code 55 Zadox growth stage), hormone foliar application was performed three times per week. Foliar spraying was done at sunset. To improve absorption, five ml of diluted Tween 20 (0.1%) was added to each 20-liter sprayer. 10 days after the third spraying, a sample was taken and the traits were measured in order to determine their value. The application of cytokinin significantly increased photosynthetic rate, leaf area index durability, weight per thousand grains, biological yield, and grain yield. The application of cytokinin had no significant impact on the greenness index of the Falat, Karaj 3, Roshan, and Yavarus cultivars, but increased the greenness index of the Sardari cultivar by 116.2% and decreased the greenness index of the Falat cultivar by 12.0%. The Karaj 3 cultivar had the highest photosynthesis with an average of 10.6 μmol.m-2.s-1 net CO2 assimilation rate, while the Falat cultivar had the lowest photosynthesis with 6.46 μmol.m-2.s-1 net CO2 assimilation rate. The application of cytokinin increased the leaf area index duration of the Falat, Karaj 3, and Yavarus cultivars while having no effect on the other cultivars. The foliar application of cytokinin had no effect on the number of seeds per plant, but there were significant differences in the number of seeds among the cultivars studied. The cultivars Karaj 3 and Yavarus had the highest and lowest seed yields per plant, with 172.6 and 83.7 seeds per plant, respectively. The foliar application of cytokinin increased the final grain dry weight of the Azadi, Roshan, and Yavarus cultivars by 5.6%, 14.8%, and 6.2%, respectively, but had no effect on the Karaj 3, Falat, and Sardari cultivars. The Azadi cultivar with an average of 1.08 mg/day and the Sardari cultivar with an average of 1.55 mg/day had the lowest and highest grain filling rates, respectively, among the cultivars studied. Except for the cultivar Roshan, the application of cytokinin increased during the grain filling period of all other cultivars. Compared to the control treatment, cytokinin increased the one-thousand seed weight by 5%. Cytokinin increased the weight of one-tousand seeds by 5% compared to the control treatment. The application of cytokinin increased the yield of the Yavarus, Karaj 3, and Sardari cultivars by 23.7%, 30.1%, and 65.5%, respectively, but had no effect on the yield of other cultivars. In the absence of cytokinin application, Azadi had the highest grain yield at 5700 kg/ha, while Roshan had the lowest at 3100 kg/ha. The application of cytokinin had no significant effect on the harvest index. The Sardari and Yavarus cultivars had the highest and lowest harvest indices (31.4% and 25.1%, respectively), whereas the harvest indices of the other cultivars did not differ significantly. Morphological, physiological, and yield-related traits differ among wheat cultivars, as demonstrated by the results of the present study. The results demonstrated that the response of wheat cultivars to cytokinin application was highly variable, and that hormone application may be ineffective or have a negative impact on certain traits.