Manuka, Leptospermum scoparium, is an medicinal and aromatic shrub from Australasia. Its phytochemical composition has been studied extensively. The essential oil from manuka has strong pre- and postemergence herbicidal activity and causes bleaching of the foliage in treated plants. Manuka oil and its primary active ingredient, leptospermone, are stable in soils for up to 7 days, though it is sensitive to microbial degradation. Leptospermone is produced in special structures called schizogenous glands within the mesophyll of the foliage. Structurally, leptospermone has a number of characteristics of conventional herbicides, which leads it to be suitable for root uptake and translocation to the foliage, where its molecular target site, p-hydroxyphenylpyruvate dioxygenase (HPPD), is located. However, leptospermone is also sensitive to metabolic degradation in planta. HPPD is a key enzyme in the biosynthesis of prenyl quinones (plastoquinone) and tocopherols and its inhibition leads to bleaching because plastoquinone is an essential cofactor for the activity of phytoene desaturase. The systemic activity of manuka oil addresses many of the major limitations normally associated with natural herbicides, such as its action being more than non-selective burn-down herbicide with higher efficacy. Additionally, its soil persistence opens up a multitude of new possibilities for the use of manuka oil as a tool for weed management and may be a potential bridge between traditional and organic agriculture.

β-Triketones from Leptospermum scoparium as natural herbicides Inhibiting p-hydroxyphenylpyruvate dioxygenase

249th National Meeting (2015)

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