Local and systemic control of powdery mildew in eucalyptus using essential oils and decoctions from traditional Brazilian medicinal plants

Abstract

Eucalyptus plants cultivated in greenhouses, nurseries and clonal minigardens are vulnerable to attack of Oidium eucalypti (powdery mildew). Essential oils and decoctions prepared from the traditional Brazilian medicinal plants Aloysia gratissima, Cordia verbenacea and Hyptis marrubioides have been shown to be effective in the control of some plant diseases. In this study, the local and systemic effects of these preparations in the control of O. eucalypti were evaluated by assessing the progress of the disease in saplings of a highly susceptible hybrid population of eucalyptus (‘urocam’). The systemic effects were also assessed by investigating the ability of the preparations to induce disease resistance, as indicated by increased peroxidase activity. The natural products were found to be as effective as a commercial fungicide (mixture of pyraclostrobin and epoxiconazole) for the control of O. eucalypti in eucalyptus plants under greenhouse conditions. Additionally, the essential oil and decoction of A. gratissima were able to exert systemic control over O. eucalypti and induce peroxidase activity in Oidium‐inoculated plants. Scanning electron microscopy revealed that the oils and decoctions from the three species exhibited direct fungitoxic activities on O. eucalypti as shown by lysis of hyphal walls and shrinking of conidia. The results presented herein suggest that oils and decoctions from A. gratissima, C. verbenacea and H. marrubioides may offer an effective, practical and ecofriendly strategy for the control of O. eucalypti in eucalyptus.