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Understanding the potential role played by major flavonoid components of apple leaves in plant defense against herbivorous arthropods
Field, greenhouse, and laboratory studies were conducted with the following objectives: (1) develop an efficient extraction and analytical method for determining concentration of major flavonoids in apple (Malus domestica Borkh.) leaves, (2) determine if differences exist in levels of these components in leaves of ten apple cultivars and if these differences explain variation in cultivar susceptibility to spider mites ( Acari: Tetranychidae), (3) understand the effects of varying light and nutritional regimes on apple leaf flavonoid levels, (4) assess if the flavonoid phloridzin, when applied to bush bean plants, affects Two Spotted Spider Mite population density, and (5) Determine if summer pruning of mature, field-grown apple trees influences levels of foliar phloridzin. An efficient extraction and HPLC analytical method is presented using commonly available and least toxic solvents and an isocratic HPLC run of short duration allowing calculation of unknown concentrations with a high degree of accuracy. Different cultivars showed significant differences in mite susceptibility and in phloridzin concentration in leaves. However, phloridzin differences do not appear to explain variation in cultivar susceptibility to spider mites. Greenhouse trials indicated that phloridzin concentration was significantly lower in leaves of potted trees of the four cultivars tested under 70% shade cloth than under full sun. All cultivars responded similarly to sun or shade in regard to percent dry weight phloridzin. Nutrition treatments appeared to have an effect on phloridzin levels only in 1995. Horticultural bush bean plants (Phaeseolus vulgaris) were either sprayed or injected through a cotton wick with 0.01 M phloridzin or distilled water, and seeded with 5 gravid female Tetranychus urticae mites. Phloridzin, either when applied topically to bean plants, or when introduced into the transpirational stream via a cotton wick, resulted in smaller numbers of T. urticae compared to plants which were not treated with phloridzin. Summer pruning of mature, field grown “McIntosh” apple had no effect on phloridzin concentration, likely indicating that summer pruning is not a stimulus of induced changes in flavonoid content.
Agronomy|Botany|Plant pathology|Plant propagation
Coli, William Michael, "Understanding the potential role played by major flavonoid components of apple leaves in plant defense against herbivorous arthropods" (2003). Doctoral Dissertations Available from Proquest. AAI3078674.