Indigenous bacteria enhance growth and modify essential oil content in Leptospermum scoparium (mānuka)

Abstract

Leptospermum scoparium J.R.Forst. et G.Forst. var. scoparium (Myrtaceae), or mānuka, is a New Zealand medicinal plant that yields essential oils with varying triketones concentrations. The effects of mānuka-associated bacteria, isolated from plants growing in five regions, on growth and essential oil composition of one regional variety, were investigated for the first time. Leaf essential oil compositions and yields were determined by microscale solvent extraction and GC-MS analyses. Erwinia sp. T4MS11P and Pseudomonas sp. M3R43 increased growth compared to control plants. Plants inoculated with Erwinia sp. T4MS11P had similar concentrations of triketone grandiflorone as control plants, whereas plants inoculated with Pseudomonas sp. M3R43 had lower grandiflorone concentrations. In contrast, inoculation with a bacterial consortium isolated from the West Coast did not increase plant growth, but gave higher grandiflorone concentrations (> 160%) compared to control plants. The different treatments showed some effects on qualitative oil composition, but these were not significantly different between regional chemotypes. Overall, the results demonstrated that bacteria increased the growth of mānuka and grandiflorone concentrations in leaves. These effects would be valuable in commercial essential oil production from plantation-grown mānuka.