Effect of potassium and calcium in nutrient solution on susceptibility of rose cut flower to gray mold disease

Gray mold, caused by the fungus Botrytis cinerea, is one of the important diseases of cut roses in Iranian greenhouses. In order to investigate the effect of different concentrations of potassium and calcium in the nutrient solution on the susceptibility of cut roses to this disease, a factorial experiment was conducted in a randomized complete block design with two factors of potassium and calcium concentrations in the nutrient solution in four replications in the greenhouse of the Safi Abad Agricultural Research Center for one year from 2007. Potassium levels were 0.1, 0.5, and 0.10 mM and calcium levels were 1.6 and 4.8 mM. During two consecutive flowering periods, harvested rose flowers were inoculated with a suspension of 104 spores per ml of B. cinerea isolate, and then the sensitivity of the flowers to gray mold was measured. The results showed that the application of potassium in the nutrient solution at a level of 0.10 mM resulted in a significant increase (p <0.01) in the severity of the disease gray mold of roses (30.4%/day) compared to the levels of 0.1 mM (24.8%/day) and 0.5 mM (26.2%/day), which was due to a decrease in the calcium concentration of the petals. A positive correlation was observed between the ratio of potassium to total cations in the nutrient solution and the severity of the disease (*r = 0.94). Also, by increasing the calcium content in the nutrient solution from 1.6 to 4.8 mM, the severity of the disease decreased from 29.6 to 24.6%/day (p <0.01). Therefore, balanced application of potassium and calcium in nutrient solutions (0.5 and 4.8 mM, respectively) is recommended for rose production under water‏cultivation conditions to prevent the effects of incompatibility between them and reduce the damage of rose gray mold disease.