Abstract
Epicuticular lipids of the foliage of four evergreen azalea hybrids ( Rhododendron spp.) and one deciduous species, R. canescens (Michaux) Sweet, were extracted and characterized by gas chromatography-mass spectrometry. Each azalea hybrid and the deciduous species had a distinct epicuticular lipid composition. The most dominant epicuticular lipid components were triterpenoids, comprising 19–47% of the surface lipids for the five azaleas. For each cultivar and for R. canescens, the major triterpenoid was ursolic acid (11–30% of total epicuticular lipids). Two triterpenoid components, α- and β-amyrin, previously implicated as insect feeding and/or oviposition deterrents, were present in lower levels in cultivars more susceptible to damage by the azalea lace bug ( Stephanitis pyrioides), a herbivorous pest of evergreen and deciduous azaleas. Scanning electron microscopy revealed distinct differences between the adaxial and abaxial surfaces of azalea leaves. Wax crystals were only seen on the lower surface of the leaves of ‘Hino Crimson’, the cultivar most susceptible to the azalea lace bug.
Published Version
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