Arbuscular mycorrhizal fungi associated with Leptospermum scoparium (mānuka): Effects on plant growth and essential oil content

Abstract

Leptospermum scoparium or mānuka is a New Zealand native medicinal plant that produces essential oils with antimicrobial properties. This study investigated the arbuscular mycorrhizal fungi (AMF) community in mānuka by culture dependent (trap culture) and independent (denaturing gradient gel electrophoresis) approaches. Furthermore, to assess whether mycorrhizal inoculation could alter growth and essential oil composition of mānuka, plants of a single regional chemotype were grown in unsterilized soil and inoculated with five AMF isolates. Leaf essential oil compositions and yields were determined by microscale solvent extraction and gas chromatography-mass spectrometry (GC-MS) analysis. AMF inoculation significantly increased growth compared to uninoculated plants. Qualitative i.e. different relative proportions of compounds, which are distinctive in chemotypes and quantitative (i.e. absolute concentrations of compounds, expressed as mg/g of dry leaf or equivalent) effects of AMF inoculation on mānuka essential oil composition depended on the isolate. AMF inoculation modified the Gammaproteobacterial community on roots and this may have contributed to changes in essential oil composition. Overall, these results demonstrated that AMF can improve the growth of mānuka and affect plant secondary metabolites in leaves, which would be valuable in commercial essential oil production from plantation-grown mānuka.