Document Type : Research Paper
Authors
1 Department of Plant Production and Genetics, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran.
2 Department of Plant Science, Faculty of Agricultural and Environmental Sciences, McGill University, Montreal, Canada.
Abstract
Objective: Exogenous application of salicylic acid improves photosynthetic efficiency and yield, while modifying the fatty acid composition of safflower seed oil under heat stress. Therefore, this study aimed to evaluate the potential of salicylic acid to mitigate the adverse effects of terminal heat stress on safflower by enhancing photosynthetic performance and optimizing seed oil fatty acid composition.
Methods: To evaluate the effects of foliar-applied salicylic acid on photosynthetic properties and fatty acid composition in safflower, a field experiment was conducted during the 2018–2019 cropping season at Shahid Chamran University of Ahvaz. The experimental design was a split-plot factorial arrangement based on a randomized complete block design (RCBD) with three replications. The main plots consisted of two sowing dates: 11th December (normal sowing) and 21st January (late sowing), while the sub-plots included a factorial combination of salicylic acid concentrations (0 and 400 μM) and two safflower cultivars: Parnian (heat-sensitive) and Faraman (heat-tolerant). Late sowing date, exposed flowering and grain filling periods to severe heat stress towards the end of the growing season.
Results: The results showed that heat stress induced by late sowing time significantly reduced key photosynthetic traits, including photosynthetic rate, stomatal conductance, transpiration, substomatal CO₂ concentration, carboxylation efficiency, and photosynthetic water use efficiency. Foliar application of salicylic acid mitigated the negative effects of heat stress on these traits. The highest stomatal conductance (711 mmol.m-². s-1), carboxylation efficiency (1.079 mmol.m-². s-1), and grain yield (3120 kg. ha-1) were observed in the Faraman cultivar sown in normal date and treated with 400 μM salicylic acid. The response of stearic acid to heat stress varied between the two cultivars, decreasing in the Faraman and increasing in the Parnian cultivar. The percentage of stearic acid changed differently under heat stress in the two studied cultivars: it decreased by 48% in the Faraman cultivar, whereas it increased by 64% in the Parnian cultivar. Notably, foliar application of salicylic acid, particularly under late sowing, increased oleic and linoleic acid percentages while reducing the linolenic and palmitic acid percentages.
Conclusion: In this study, safflower cultivars experienced changes in photosynthesis traits, grain yield and fatty acid compositions under high temperature conditions. Foliar application of salicylic acid mitigated the adverse effects of heat stress by improving photosynthetic performance and modulating fatty acid composition, thereby enhancing heat tolerance and improving oil quality in both cultivars. These benefits were more pronounced in the heat-tolerant Faraman cultivar compared to the control.
Keywords
)