Abstract
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. lactucae on 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.
Highlights
Downy mildew caused by the oomycete Bremia lactucae Regel is the most serious disease in field and greenhouse lettuce production [1]
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 suitable biopesticide for its control
The disease can be controlled by synthetic chemicals, including protective and systemic fungicides such as phenylamide, strobilurins, and CAA-based compounds
Summary
Downy mildew caused by the oomycete Bremia lactucae Regel is the most serious disease in field and greenhouse lettuce production [1]. A low level of infection can downgrade the crop, causing significant losses at harvest, and can promote decay during postharvest transit and storage; whereas a high level of disease can render a crop unmarketable [2]. Controlling the disease in organic production is dependent on a small number of approved products, including copper hydroxide. Use of this heavy metal may have long-term consequences due to its accumulation in soil [4]. The disease can be controlled by synthetic chemicals, including protective and systemic fungicides such as phenylamide (e.g., metalaxyl/mefenoxam-based compounds, and phosphites). Isolates that are insensitive to these compounds are common [5,6]
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