Postharvest Quality of Roses under Different Levels of Nitrogenous Compounds in Holding Solution

Nitrogen (N) forms and N levels can have a great impact on growth and quality of agricultural crops. Postharvest N treatments may also affect the quality of products. This study was conducted under laboratory conditions to evaluate the changes in postharvest quality characteristics of cut roses (Rosa hybrid cv ‘Utopia’) under different nitrogen concentrations of holding solution. Three nitrogen sources including ammonium sulfate, calcium nitrate and potassium nitrate at five concentrations (0, 5, 10, 15 and 20 mgL-1 N) were applied into vases with holding solution. The results showed that low ammonium (5 mg L-1) and high nitrate (20 mgL-1) resulted in the highest leaf SPAD values, whereas the lowest values were recorded for those stems treated with the two highest ammonium concentrations (15 and 20 mg L-1). Leaf and petal relative water contents (RWC) were significantly reduced by higher ammonium concentrations, while they were increased by increasing calcium nitrate and potassium nitrate concentrations in the vase holding solution. Leaf catalase activity was increased by the two lowest (5 and 10 mg L-1) and decreased by the two highest ammonium levels (15 and 20 mg L-1), and it was not affected by the two other nitrogen salts. Higher ammonium levels resulted in a significant increase in leaf proline concentrations and petal ion leakage, whereas nitrate concentrations reduced these two traits. A low concentration of ammonium (5 mg L- 1) increased flower vase life while higher ammonium concentrations reduced the trait. There was also an increasing trend in flower vase life with higher concentrations of both nitrate salts. Therefore, low ammonium or high nitrate levels in vase holding solution can improve vase life quality of cut roses