2.3 Pathogen
P. expansum was originally isolated from symptomatic pear fruits. The pathogen was cultured in a test tube with potato dextrose agar (PDA; con- sisting of 200 ml boiled potato extract, 20 g glucose, and20gagarin1Lofdistilledwater)at28°Cfor7d. Conidia were removed by rubbing the surface of the medium with a bacteriological loop and suspending the loop in sterile distilled water. The final spore concentration was adjusted to 1×104 spores/ml by use of a hemocytometer.