Seasonal changes in phenolic compounds in the leaves of scab-resistant and susceptible apple cultivars

Mikulic Petkovsek, M., Stampar, F. and Veberic, R. 2009. Seasonal changes in phenolic compounds in the leaves of scab-resistant and susceptible apple cultivars. Can. J. Plant Sci. 89: 745-753. Leaf samples were collected from apple varieties susceptible and resistant to apple scab [Venturia inaequalis (Cke.) Wint.] from June to September for 2 yr between 2005 and 2006. These were analyzed for phenolic compounds, using high-performance liquid chromatography (HPLC). In the apple leaves, the following hydroxycinnamic acids were detected: chlorogenic, caffeic and p-coumaric acids; the following dihydrochalcone: phloridzin, and the following flavonoids: epicatechin, catechin, rutin and quercitrin. The total of phenolic compounds in apple leaves was determined spectrophotometrically, using the Folin-Ciocalteu method. During the growing season, the content of phenolic compounds changed and was related to the physiological stage of the tissue and cultivar used. Each phenolic compound had its own curve of seasonal changes in concentration. In 2005 there was no significant change in total phenols during the growing season. In 2006, their content changed significantly during the growing season; statistically the highest content of total phenols was found in the leaves in August. Total phenols as well as single phenolics were statistically higher in resistant than in Susceptible apple varieties for both years.