| Summary: | Bitter apple (Citrullus colocynthis), a desert plant with medicinal properties, typically exhibits low seed germination due to dormancy. This study investigated physical and chemical treatments to improve C. colocynthis seed germination. A completely randomized design with factorial arrangement and three replications was used to test the effects of gibberellic acid (GA3) at concentrations of 0, 10, 50, 100, and 150 ppm, under four diurnal temperature and light (TL) regimes: (1) 20°C (12h light/dark), (2) 25°C (12h light/dark), (3) 35°C (12h light) / 15°C (12h dark), and (4) 30°C (12h light) / 20°C (12h dark). Results showed that TL regime, GA3, and their interaction significantly affected all measured germination parameters. The highest germination percentage, relative germination percentage, mean daily germination, germination index, germination value, and seedling dry mass were achieved with 100 ppm GA3 under the 35-15°C regime. The study concluded that average germination speed, germination time variation coefficient, germination speed coefficient, and synchronization index were unreliable for assessing seed quality under low germination conditions, suggesting that physiological dormancy in Bitter Apple seeds may stem from embryo immaturity, inhibitory factors, or both.
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