Morpho-physiology of sour orange seedling treated with melatonin under in vitro water stress

The study was conducted in the Micropropagation laboratory, Faculty of Agriculture, University of Kufa, from November 2023 to March 2024 to study the in vitro effects of Polyethylene glycol (PEG) in sour orange (Citrus aurantium) seed germination and seedlings growth using growth chamber seed culture. Mature sour orange seeds were cultured on Murashige and Skoog medium supplemented PEG 6000 at concentrations of 0, 0.5, or 1 % and 3 concentrations of melatonin (0, 0.5 or 1 mg L-1) for 45 days to study water stress effect on seed germination percentage, seedling length, root length, fresh weight and dry weight. Results showed that water stress adversely affected these traits: seed germination percentage, seedling height, fresh and dry weight and root length, alongside the increase in PEG concentration compared to PEG 6000 free medium after 45 days of the seed culture. The nutrient medium supplemented with melatonin reduced the negative effect of water stress as it improved seed germination rate, seedling height, shoot fresh and dry weight and root length, as the concentration exceeded 1 mg L-1. All the study indicators were significantly affected by the interaction treatments of PEG and melatonin, especially in the absence of PEG. Particularly, the interaction of 0 % PEG plus 1 mg L-1 melatonin produced the highest values ​​in all plant growth traits studied, while the interaction treatment at 1 % PEG with 1 mg L-1 melatonin gave lower values in the traits abovementioned.