Abstract Roses (Rosa sp.) are one of the important ornamental species due to its high value and production, and its high demand worldwide. In roses, fertilization programs significantly affected yield, quality, and postharvest physiology, especially for nitrogen (N) and potassium (K) nutritions. Therefore, it is necessary to identify the optimum levels of mineral nutrients for the commercial production of cut flower roses in a hydroponic system to improve shoot growth and flower quality and to avoid the accumulation of undesirable ions in the root zone. This study was aimed to eva‎luate the effect of different levels of nitrogen (N) and potassium (K) in nutrient solution on flower characteristics and the vase life of cut flowers of rose. This study was conducted in two separate expriments from April to June 2020 and from August to October 2020 in a commercial Quonset-type greenhouse located at Najafabbad, Isfahan, Iran. Rooted cuttings of Dolcevita cultivar, as a promising and large-flowered rose, was used as the plant material in this experiment. The rooted cuttings, when two true leaves appeared, were planted in substrate including cocopit and perlite (1:1 ratio) into a hydroponic system. A total of 15 plants per treatment, including three replications, were planted at a density of 15 × 30 cm2 (8 plants/m2). The treatments were set in a completely randomized design (RCBD). Each treatment differed in the composition of one nutrient, N (100, 150, 200 mg•L -1 ) and K (150, 200, and 250 mg•L -1) with the other nutrients held constant. Results showed that number of cut flower per plant, cut flower length, stem dimeter, and flower length significantly affected by different ratios of nitrogen and potassium. Rising the concentration of nitrogen in the nutrient solution increased the number of flower branches per plant, while the length and diameter of the flower branch increased with increasing potassium content, especially in nutrient solutions containing 150 mg /l nitrogen. The highest branch length and diameter as well as bud length were observed in T5 treatment (containing 150 mg/l nitrogen and 200 mg/l potassium). The amount of anthocyanin in the petals increased significantly with increasing potassium levels in the nutrient solution, while no significant changes were observed in terms of photosynthetic pigments chlorophyll and carotenoids. Changes in the amount of nitrogen and potassium in the nutrient solution caused significant changes in the concentration of elements in the cut flower, especially nitrogen and potassium. However, no significant changes were observed in the amount of calcium and magnesium in the tissue. The results revealed that the combination of different concentrations of nitrogen and potassium in nutrient solution was effective in water relations and vase life of flowers so that flowers harvested from plants grown in nutrient solution T5 and T6 containing medium concentration of nitrogen (150 mg /l) in combination with medium and high concentrations of potassium (200 and 250 mg /l) had the highest solution absorption and water balance as well as vase life. In conclusion, based on the results obtained from this experiment, moderate concentrations of nitrogen (150 mg/L) in combination with moderate and high concentrations of potassium (200 and 250 mg/L) in nutrient solution (T5 and T6) improved the quality characteristics of cut Rose flowers including flower length, stem and flower diameter, flower stem weight and petal anthocyanin content, which improved water relations and vase life, which can be effective in crop marketing.

نعمت اله اعتمادي، علي نيك بخت

حسين شريعتمداري

بهرام باني نسب،مهران شيرواني