The Effect of Calcium Chloride Sprays on Botrytis cinerea Infection of Petunia x hybrida Flowers in the Postharvest Environment.

Botrytis cinerea causes rapid decay of Petunia x hybrida flower petals in the postharvest environment. The objective of this experiment was to find alternative methods to improve resistance of petunia flowers to botrytis growth. Four concentrations of calcium chloride (0, 400, 800, or 1200 ppm) spray applications were made to flowering petunias over two weeks. A fungicide application (cyprodinil and fludioxonil) (0.45 g/l) provided an additional control. Twenty-four hours after the final calcium chloride application, flowers were removed from the plants and placed into a chamber (six flowers per chamber) with 99% humidity and inoculated with a conidial suspension (1x 10⁴ conidia/ml). The botrytis isolate used was resistant to the two fungicides. Data were collected on the progression of the fungal disease for 72 h at 12-h intervals. Flowers were scored using a 1 to 9 scale based on disease progression, 1 having minimal necrosis and 9 being complete loss of tissue integrity. The calcium chloride application of 1200 ppm had the highest resistance to botrytis infection with a disease severity score of 2 after 72 h following inoculation. In comparison, the calcium chloride 800 ppm treatment had disease severity score of 7 at 72 h. The fungicide treatment proved least effective with a score of 9 at 72 h. These results demonstrate the potential benefit of calcium chloride spray applications for the management of botrytis infection during the post harvest of flowering petunias.