Enhanced Resistance to Side Rot in Pears Treated with Calcium Chloride During the Growing Season. David Sugar, Oregon State University, Southern Oregon Experiment Station, 569 Hanley Road, Medford, OR 97502. Kate A. Powers, and Richard J. Hilton. Oregon State University, Southern Oregon Experiment Station, 569 Hanley Road, Medford, OR 97502. Plant Dis. 75:212-214. Accepted for publication 17 September 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0212.

Incidence and severity of side rot in Bosc pears were reduced in fruit from trees treated with CaCl₂ sprays during the growing season. Trees were treated every 2 wk beginning in early July for a total of three applications of CaCl₂ at 0, 1.2, 3.6, or 6.0 g/L of calcium. Mature fruit were wound-inoculated postharvest with spore suspensions of Phialophora malorum at 0, 10, 10², 10³, or 10⁵ spores per milliliter. Lesion diameter was measured after 3 mo of storage at 0 C. A significant interaction between rate of CaCl₂ and spore concentration was observed. At 6.0 g/L of calcium, the mean area of decay was reduced at spore concentrations >10² per milliliter. At 3.6 g/L of calcium, lesion area reduction was significant at 10² and 10⁵ spores per milliliter. At 1.2 g/L of calcium, lesion area reduction was significant only at 10² spores per milliliter. CaCl₂ treatment reduced incidence of side rot in naturally infected fruit in 3 yr of trial. CaCl₂ did not reduce incidence of decay of pear by Penicillium expansum. Calcium concentration in mature fruit peels was related to level of CaCl₂ treatment.