Effects of three potassium salts for the control of Penicillium expansum and Botrytis cinerea on apples

The effects of potassium silicate, potassium chloride and potassium hydroxide for the control of postharvest gray and blue molds were tested on 'Golden Delicious' apples. The incidence of gray mold and blue mold was significantly (P≤0.001) reduced by the application of potassium silicate, potassium chloride and potassium hydroxide on wounds of apple fruit. Fruit treated with potassium silicate at a concentration of 100,000 mg L^‑1 had the lowest incidence of gray and blue molds (77.5 and 65%, respectively) when it was applied as a preventative treatment (24 h before inoculation with either Penicillium expansum or Botrytis cinerea). Scanning electron microscopy studies confirmed that potassium silicate applications to apple wounds stopped germination of conidia of both B. cinerea and P. expansum. Curative treatment (inoculated with either P. expansum or B. cinerea 4 h before treatment) of apples with potassium silicate at a concentration of 100,000 mg L^‑1 resulted in reduced incidence of gray and blue molds (52.5 and 55%, respectively). Both potassium chloride and potassium hydroxide reduced the incidence of blue mold (77.5 and 70%, respectively) and gray mold (65 and 62.5%, respectively) on 'Golden Delicious' apples when applied as a preventative treatment (24 h before inoculation with either P. expansum or B. cinerea).