Document Type : Original Article
Authors
1 Shahid Bahonar University of Kerman
2 Shahid Bahonar university of Kerman
3 Head of Genetic and Plant Production Dep.
Abstract
To investigate the effects of brassinosteroid and melatonin on antioxidant enzymes and yield of quinoa under drought stress, a split-plot experiment based on a randomized complete block design was conducted during the 2019–2020 and 2020–2021 growing seasons at the Research Farm of Shahid Bahonar University of Kerman. Treatments included three irrigation levels (100, 75, and 50% of field capacity) as the main plots, and nine foliar applications as subplots. Drought stress, foliar application, and their interactions significantly affected physiological traits and yield. Increasing drought enhanced malondialdehyde (MDA) content and polyphenol oxidase, while reducing leaf protein. The highest MDA obtained under no foliar application with 50% field capacity irrigation (36.52% increase), whereas foliar application under 75 and 50% irrigation significantly reduced it. The lowest leaf protein was also observed under no foliar application at 50% field capacity (22% reduction). The maximum catalase occurred under 75% irrigation with foliar application of 0.5µM melatonin × 0.5µM brassinosteroid, while the minimum was under 50% irrigation without foliar application. Combined foliar spraying increased peroxidase activity (up to 0.83%) compared with the control. Drought stress significantly enhanced polyphenol oxidase, with the highest activity (25% increase) recorded at 50% field capacity. Grain yield was strongly affected, with the highest yield under 100% irrigation and the lowest under 50% in the second year. Combined foliar application of melatonin and brassinosteroid, particularly under stress (75 and 50%), significantly improved yield by up to 65% compared with the control, with higher concentration being more effective under severe drought.
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