Essential Tea Tree Oil Activity against Bremia lactucae in Lettuce

Downy mildew caused by the oomycete Bremia lactucae Regel is a serious disease of lettuce in field and greenhouse production. Here we report on the antifungal activity of essential Australian tea tree oil (TTO) derived from Melaleuca alternifolia against downy mildew in lettuce. Preventive treatments with Timorex Gold (STK Ltd., Petach Tikva, Israel), fungicide containing TTO, suppressed the development of B. lactucaeon cotyledons and young lettuce plants. Epifluorescence microscopy showed that TTO had a moderate inhibitory effect on spore germination of the pathogen but a strong inhibitory effect on sporophore emergence and hence on sporulation. Timorex Gold (22.3 EC W/V) was as effective as copper hydroxide in controlling the disease in organic field plots. It was as effective as the fungicides Bellis (Boscalid + Pyraclostrobin; BASF, Germany) and Commet (pyraclostrobin; BASF, Germany) in conventional production. The results demonstrate that Timorex Gold effectively suppresses the development of downy mildew in lettuce in growth chambers as well as in the field, and thus suitable biopesticide for its control.