2018 ASHS Annual Conference

Previous research has demonstrated that Botrytis infection of petunia flowers decreases when calcium levels increase in the petal tissue. The objective of this experiment was to determine the optimal method to deliver calcium to petunia flower petals. The two methods tested were: 1. supplying calcium in the fertigation solution, and 2. supplying calcium in spray applications using calcium chloride. A two-factor factorial design was used to test both methods. All nutrients in the fertigation treatments remained the same except for calcium, sodium and chloride. The fertigation treatment provided calcium concentrations of 0, 100, and 200 mg·L^-1 for 3 weeks prior to flower opening. The spray applications provided calcium concentrations of 0, 750, and 1500 mg·L^-1 once a week for 3 weeks. Growing medium, leaves, and flowers were analyzed for calcium content to determine the effect of application method and concentration on the tissue calcium concentrations. Botrytis efficacy trials determined which treatment method provided the most plant resistance to Botrytis infection upon inoculation. The results showed that increasing calcium concentration in the fertigation solution improved the calcium concentration in the leaves but not the flowers. Spray applications of calcium significantly increased the calcium concentration of the flower petals compared to the fertigation treatments and also had the lowest incidence of Botrytis infection. These results demonstrate the benefit of using calcium chloride spray applications to increase calcium content in reproductive tissue and increase petunia flower petal resistance to Botrytis infection.