Effect of Different Concentrations of Gibberellic Acid on the Growth of Euphorbia Pulcherrima

Author(s): Rony El Khoury, Soumaya Naser el deen, NaimBoustany, Georges Abi Rizk, Leila Geage

Gibberellic acid is one of the growth hormones used for poinsettia (Euphorbia pulcherrima) to stimulate the elongation, the cell division and the formation of longer internodes. Four hundred and twenty plants of Euphorbia pulcherrima, imported from Italy, were pinched and distributed into 7 blocks (block T, A, B, C, A ', B' and C'). Each block is made up of 15 plants distributed randomly. The treatments consisted of spraying gibberellic acid at different concentrations of 5 ppm, 10 ppm, and 50 ppm on poinsettia plants, once (blocks A, B, and C) or twice (A', B' and C' blocks). The blocks T are control plants. Five parameters were measured: the height of the plant, the height of the main branch and its diameter, the number of lateral shoots, the number of bracts per shoot.The application of a high concentration of the hormone (50 ppm) early in the season (October 15, 2015) and 3 weeks later influenced, strongly, the height of the plants (38.4 cm) and that of the main branches (33.83 cm). These results were significantly different from those obtained in all other treatments at P<0.05. On the other hand, the 3 concentrations of GA did not influence neither the diameter of the main branches, nor the number of lateral shoots or the number of bracts at P>0.05.Moreover, the study of correlation showed that the height of the plants had a strong positive correlation (P<0.001) with the height of the main branch.