Interaction effects of cytokinin hormone and heat stress on yield and morphophysiological traits in barley (Hordeum vulgare L.) cultivars adapted to tropical regions

Global climate change has heightened the occurrence of heat stress, significantly impacting agricultural productivity, especially in tropical regions. This study investigates the interaction effects of cytokinin application and heat stress on the growth and biochemical traits of barley (Hordeum vulgare L.) cultivars adapted to tropical climates. The experiment was conducted over two growing seasons (2021–2022 and 2022–2023) using a split-split plot design with three replications. The primary treatments included two planting dates (normal and delayed), three cytokinin levels (control, 50 μM, and 100 μM), and five barley cultivars (Oksin, Nowruz, Nimroz, Zahak, and Golchin). The results showed that cytokinin application, particularly at 100 μM, significantly enhanced photosynthetic pigment retention, catalase activity, and the accumulation of secondary metabolites such as flavonoids and anthocyanins. Additionally, cytokinin-treated plants exhibited higher protein content and reduced malondialdehyde (MDA) levels, indicating better membrane stability and reduced oxidative damage under heat stress. Cultivars Nowruz and Zahak demonstrated the highest resilience to heat stress across both planting dates. These findings indicate that cytokinin is an effective tool for enhancing heat stress tolerance in barley by improving key physiological and biochemical processes. The hormone's ability to enhance photosynthetic efficiency, antioxidant defenses, and secondary metabolite production provides a practical strategy for improving crop resilience in regions affected by rising temperatures due to climate change.