Makka Hassan, Hani Saber Saudy, Mohammed Hewidy, Heba El-Sammak
PURPOSE: Stimulating flowering ability is the main purpose of commercial development of ornamental plants. Colchicine could contribute to improve flowering and related physiological processes; however its potential mode on marigold (Calendula officinalis) as a marketable ornamental plant is unclear. METHODS: The present study was carried out during two successive generations (M1 and M2) along two experimental seasons of 2019-20 and 2020-21 at the nursery conditions. Shoot-tip seedlings of marigold were treated by different concentrations of colchicine (0.00, 0.025, 0.050, 0.075 and 0.100%) to study its effect on the morphological traits, phytochemical composition as well as identifying the possibility of mutations induction using ISSR marker technique. RESULTS: Non-significant variations in survival rates were obtained among the tested colchicine concentrations, while a noticeable decline in germination percentage was observed as colchicine concentration increased. Application of colchicine at concentrations of 0.025% and 0.075% possessed the highest values of total carbohydrates content and phenols content, respectively, in both M1 and M2 generations. In M1 generation, application of 0.025% colchicine was the superior treatment for stimulating all inflorescence attributes with lowering flowering period, while the colchicine concentrations of 0.075% or 0.100% showed the longest flowering period. In M2 generation, application of 0.100% colchicine achieved the highest values of flowering date and inflorescence attributes, while the longest flowering period was obtained with application of 0.025% colchicine. Both 0.050% and 0.100% concentrations showed abnormal and multiplied branching. CONCLUSION: Some variations in the habit of growth, leaf form and inflorescence structure were observed in both generations with application of colchicine. Commercially, using colchicine at 0.025% as growth stimulator is regarded as an effective practice for avoiding growth abnormality, while obtaining marketable marigold flowers. Also, ISSR marker- PCR technique was able to detect colchicine-caused mutations in marigold plant.