Morphological and cytological studies of diploid and colchicine-induced tetraploid lines of crape myrtle ( Lagerstroemia indica L.)

Abstract

The tips of cotyledon-stage seedlings of three crape myrtle cultivars (“Zi Wei”, “Hong Wei” and “Yin Wei”) were treated with colchicine. Various concentrations of colchicine and different treatment durations were tested. Seedlings of “Zi Wei” treated with 0.5% colchicine for 72 h and seedlings of “Yin Wei” treated with colchicine (0.2% for 96 h, 0.5% for 48 h and 0.8% for 72 h) demonstrated high rates of mutation; “Hong Wei” showed a slightly lower rate. The highest rate of morphological variation was 54.17% and this was achieved when tips were treated with 0.5% colchicine for 72 h. Putative tetraploid plants were identified with morphological and cytological variations, such as larger and thicker leaves, darker green coloration, larger stomata, lower density of stomata across the lower leaf epidermis and increased numbers of chloroplasts per stomata guard cell. Flow cytometric analysis demonstrated that the nuclear DNA content of 15 of these putative tetraploids (of which 7 were “Zi Wei”, 5 were “Yin Wei”, and 3 were “Hong Wei”) was indeed doubled relative to that of control diploid plants. The chromosome number of the tetraploid plants was 2 n = 4 x = 96, while that of the control diploid plants was 2 n = 2 x = 48. Ornamental characteristics were also enhanced in the tetraploid plants, with increased diameter of the individual flowers and greater basal length of the petals and claws. Pollen diameter and the size of capsules and seeds were also significantly greater than those of diploid plants.