Effect of orange essential oil and its constitutes on late blight disease of potato plants under field conditions

Late blight caused by Phytophthora infestans is the most important disease attacking potato plants. Four concentrations of essential oils i.e. 0.0, 1.25, 2.5, 5.0 and 7.5 ml/l of Orange, Citral, Methyl antranate (MA), and Terbinol were tested for controlling late blight disease. Results indicate that all treatments except orange oil have an inhibitory effect against the linear growth of P. infestans. Complete reduction in linear growth was obtained with Citral and MA at concentrations of 5.0 and 7.5 ml/l. Other treatments showed moderate effect against P. infestans. In greenhouse experiments, results indicate that all treatments have protective and therapeutic effects against late blight disease except Orange oil which has a protective effect only. High reduction was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which reduced the disease severity by more than 77.1 and 62.8% when applied as protective and therapeutic treatments respectively. Moderate effect was obtained with orange oil and Citral at concentration of 7.5 ml/l for both treatments which reduced the disease severity by more than 65.7% when applied as protective treatments. Similar results were obtained under field coditions; results indicate that all treatments reduced the late blight severity during two growing seasons. High reduction was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which reduced the disease severity by more than 80.0%. As for potato yield, results indicate that all treatments increased potato yield during two growing seasons. A high increase was obtained with Citral and MA at concentrations of 2.5 and 5.0 ml/l which increased the potato yield by more than 59.1%. Other treatments showed a moderate increase. It could be suggested that some essential oils of citrus or their constituents might be used for controlling late blight disease potato plants under field conditions.