Inoculation of arbuscular mycorrhizal fungi and phosphorus addition increase coarse mint (Plectranthus amboinicus Lour.) plant growth and essential oil content

Abstract The coarse mint (Plectranthus amboinicus Lour.) is a medicinal plant that produces essential oil; however, it is still little studied the effects of effects of arbuscular mycorrhizal fungi species on growth and essential oil content and its composition in P. amboinicus. Therefore, this study aimed to evaluate Rhizophagus clarus and Claroideoglomus etunicatum under low and high phosphorus conditions and its effects in plant growth and the essential oil content and chemical composition in coarse mint. The experimental design was completely randomized with 8 replicates per treatment in a 3x2 factorial (without and with two arbuscular mycorrhizal fungi, two levels of phosphorus (at 20 or 200 mg dm–3 of substrate). We evaluated spore density in the substrate and root colonization by arbuscular mycorrhizal fungi, an also shoot and root phosphorus content and nitrogen in the shoots, plant growth, essential oil content and its chemical composition. Spore density and root colonization by arbuscular mycorrhizal fungi were higher in the inoculated treatments. The shoot dry matter, root dry matter and total dry matter increased with arbuscular mycorrhizal fungi inoculation, mainly with the inoculation of R. clarus and high addition of phosphorus to the substrate. Inoculation of arbuscular mycorrhizal fungi and/or the addition of phosphorus in the substrate increased phosphorus and nitrogen content in the plant. The essential oil content was higher with R. clarus and with low phosphorus addition (0.61%) and 18 compounds were identified in essential oil, being carvacrol (38.48-51.07%), followed by trans-Caryophyllene, α-Bergamotene and α-Humulene the major constituents. It was concluded that plant growth increased with R. clarus inoculation and high phosphorus condition and R. clarus inoculation increased essential oil content.