The effect of foliar application of cytokinin and salicylic acid on yield and physiological characteristics of sunflower under drought stress conditions

Background and Objective: Oil is one of the main food items needed by humans. More than 90% of oil in the country is supplied through imports. Sunflower is an oil seed that can be cultivated twice a year in Khuzestan. Drought stress reduces the relative water content , increases stomatal resistance, and as a result, the amount of photosynthesis ,oil and seed yield decreases. The goals of study were to recognize the effects of spraying of Cytokinin and Salicylic Acid, on Physiological, biochemical and Yield of Sunflower On Drought Stress.

Materials and Methods: The experiment was conducted as split plot based on randomized complete blocks design with three replications in the experimental farm of the Department of plant production genetics, Shahid Chamran University of Ahvaz, in the 2021-2022 cropping season . The main factor includes the irrigation cycle at three levels (8, 12, and 16 days) and the sub factor includes 5 hormone levels (without hormone, cytokinin hormone at two levels of 25 and 50 µmol/liter and salicylic acid at two levels 200 and 400µmol /liter).The oscar cultivar was used.

Results: The interaction of irrigation distance and hormone levels for all traits were significant at the 1% probability level. Increasing the irrigation cycle from 8 to 12 and 16 days decreases the rate of photosynthesis, stomatal conductance, leaf area index, greenness index and relative water content and increases antioxidant enzymes (catalase, peroxide and superoxide dismutase) and consequently Seed yield and seed oil yield decreased. Cytokinin and salicylic acid solution spraying in 16-day improved stress tolerance and ultimately an acceptable increase in seed and oil yield. So that the seed yield increased by 69, 72, 37 and 64% under the influence of cytokinin 25 and 50 µM/L and salicylic acid 200 and 400 mM/L respectively. Cytokinin 50 μM increased seed yield by 33, 16.5, and 72% and oil yield by 33.5, 19.5, and 50% under irrigation conditions of 8, 12, and 16 days, respectively.

Conclusion: Under stress conditions, seed and oil yields decrease, the reason for this is the decrease in leaf area index, leaf relative water content, average stomatal conductance, photosynthesis rate and chlorophyll index. With the increase of reactive oxygen species(Ros), the activity of catalase, peroxidase and superoxide dismutase increases, the external application of cytokinin and salicylic acid in the form of foliar spraying on the aerial parts of sunflower plants increases the tolerance to drought and increasing the seed and oil yield in this plant, therefore, cytokinin and salicylic acid can be suggested as a solution to improve the yield of sunflower seeds and oil in drought conditions, although both hormones were useful, but cytokinin with The dose of 50 μM was more effective. By increasing the dose of cytokinin from 25 to 50 µM/L under severe stress conditions, it caused a decrease in oil percentage and grain yield. Although the effect of cytokinin has been better, due to the high price difference of cytokinin from salicylic acid, the use of both hormones is recommended to farmers in water shortage conditions by increasing the irrigation cycle instead of 8 days to 12 days.