Mutagenic and physiological impacts of colchicine on growth, flowering behavior, and ISSR-based genetic variability in Calendula officinalis L

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. 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. 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. 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.