Biochemical changes in Quercus robur L. leaves after Erysiphe alphitoides infection

Abstract

AbstractAlthough powdery mildew caused by Erysiphe alphitoides is a major foliage diseases of young oak forest plantations, the knowledge of defence responses of the tree to infection by this pathogen is limited. We investigated biochemical changes characteristic of the defence responses in oak leaves infected to different degrees. Foliage was screened for selected reactive oxygen and nitrogen species using biochemical and histochemical methods in July, August and September over three vegetation seasons. High‐performance liquid chromatography or gas chromatograph‐mass spectrometry analyses of phenolic compounds and volatile organic compounds, respectively, were performed. Changes in the activity of the antioxidant enzymes, that is superoxide dismutase, catalase and peroxidase, were also analysed with biochemical and electrophoresis methods. Infection‐induced biochemical responses occurred in oak leaves in all months, mainly in August, including increased catalase and peroxidase activities and the accumulation of hydrogen peroxide, nitric oxide and phenolic compounds of the flavonoid and derivatives of hydroxybenzoic and cinnamic acids classes. Volatile organic compounds, including lipoxygenase products, isoprenoids and methyl salicylate, were produced with high intensity in all the infected leaves. These results suggested that enhanced production of reactive oxygen and nitrogen species, and phenolic compounds, and the involvement of antioxidant enzymes plus induced emissions of volatile organic compounds may be essential components of the defence response of pedunculate oak to infection by E. alphitoides.