Soybean plants sprayed with azelaic and hexanoic acids and infected by Phakopsora pachyrhizi display better photosynthetic performance and a robust antioxidative metabolism

This study investigated the potential of azelaic acid (AzA) and hexanoic acid (HxA) to reduce rust development, caused by Phakopsora pachyrhizi, on soybean and the physiological and biochemical changes involved. A 4 x 2 factorial experiment was arranged in a completely randomized design with four replications. The factors studied were as follows: plants sprayed with water (control), acibenzolar-S-methyl (ASM; 0.5 g/L) (a well-recognized resistance inducer), AzA (1 mM) or HxA (20 mM) that were non-inoculated or inoculated with P. pachyrhizi. Area under rust progress curve significantly decreased by 97%, 95% and 95% for ASM, HxA and AzA treatments, respectively, compared with the control treatment. Infected and AzA and HxA-sprayed plants showed less impairment on photosynthesis (moderate changes in the values of chlorophyll a fluorescence parameters linked to great concentrations of total chlorophyll a + b and carotenoids) in contrast to infected and water-sprayed plants. A more robust antioxidative metabolism (great activities of superoxide dismutase, ascorbate peroxidase, catalase, peroxidase and glutathione reductase) on infected and AzA and HxA-sprayed plants helped to reduce hydrogen peroxide and anion superoxide radical depositions in leaf tissues and their concentrations. Collectively, the physiological and biochemical responses obtained for infected and AzA and HxA-sprayed plants were comparable with that obtained with ASM. Based on these findings, it is plausible to consider the potential of using AzA and HxA for rust management in soybean toward sustainable agriculture.