Relationship of Bound Calcium and Inoculum Concentration to the Effect of Postharvest Calcium Treatment on Decay of Apples by Penicillium expansum. William S. Conway, Research Plant Pathologist, USDA, ARS, Horticultural Crops Quality Laboratory, BARC-West, Beltsville, MD 20705. Kenneth C. Gross, and Carl E. Sams. Plant Physiologist, Associate Professor, USDA, ARS, Horticultural Crops Quality Laboratory, BARC-West, Beltsville, MD 20705, and Department of Plant and Soil Science, University of Tennessee, Knoxville 37996. Plant Dis. 71:78-80. Accepted for publication 5 June 1986. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/PD-71-0078.

Golden Delicious apples were pressure-infiltrated (68.95 kPa) at harvest with 0, 1, 2, or 4% solutions of CaCl₂ and stored at 0 C. After 6 mo, the fruits were removed from storage and wound-inoculated with a conidial suspension of 10⁴, 10⁵, or 10⁶ spores of Penicillium expansum per milliliter. After 7 days at 20 C, the fruits were rated for decay severity. The cell walls of similarly treated but uninoculated fruits were extracted and analyzed for Ca concentration. As the Ca concentration of the solutions with which the fruits were infiltrated increased, the amount of cell wall-bound Ca also increased. As the cell wall Ca content increased and the inoculum concentration decreased, the amount of decay decreased. These results indicate that as the inoculum concentration decreases the relative effectiveness of increased cell wall-bound Ca in reducing decay increases.