Effect of Paclobutrazol on Some Morphological and Physiological Characteristics of Petunia under Drought Stress

This experiment was conducted to investigate the effect of paclobutrazol as an anti-gibberellin on some morpho-physiological characteristics of Petunia × grandiflora ‘Bravo Blue’, and determine the optimum concentration of paclobutrazol for drought resistance in this plant. The experiment was carried out as factorial based on completely randomized design with three replications in greenhouse. The studied factors were included paclobutrazol in four levels (0, 25, 50 and 75 mg a.i. l-1) and drought stress in three levels (irrigation when soil moisture reached 90 %, 75 % and 50 % of field capacity). Results showed that the application of paclobutrazol had increased the number of flowers, aerial part dry weight and number of lateral branches, and the application of this substance decreased the plant height, root dry weight and amount of carotenoids. While, paclobutrazol did not have significant effect on the electrolyte leakage, main branch number and leaf area of petunia. Also, the results showed that drought stress increased the number of flowers per plant, and reduced the content of chlorophyll, carotenoids, flower diameter, shoot and root dry weight and leaf area of petunia. Application of 75 mg a.i.­ l-1 paclobutrazol had the greatest effect on height controlling of petunia plant under drought stress. Carotenoids and chlorophyll content was increased by increasing the paclobutrazol concentration under 50% of field capacity. Generally, the results indicated that the application of paclobutrazol under severe drought stress could prevent chlorophyll and carotenoids decline, and had partially been effective in overcoming adverse effects of drought stress.