Arbuscular mycorrhizal fungi and organic manure enhance growth and accumulation of citral, total phenols, and flavonoids in Melissa officinalis L.

• Arbuscular mycorrhizal fungi (AMFs) provided significant dry weight gain for plants. • Cattle manure source influenced the growth of Melissa officinalis. • AMFs and organic manure influenced essential oil content. • AMFs and in the presence of cattle manure contributed to the accumulation of citral. • AMFs led to the accumulation of total phenols. The use of arbuscular mycorrhizal fungi (AMFs) during cultivation is a promising possibility to increase biomass and essential oil yield of medicinal plants. The objective of the present study is to observe the influence of AMFs and fertilization with organic manure (OM) on Melissa officinalis growth, phenols, flavonoids, and on the chemical composition of its essential oil. The treatments were: (+)AMF(-)OM (with fungi and without organic manure), (+)AMF(+)OM (with fungi and with organic manure), (-)AMF(+)OM (without fungi and with organic manure), and (-)AMF(-)OM (without fungi and without organic manure)-control. Leaf (LDW), stem (SDW), root (RDW), shoot (ShDW), and total dry weight (TDW), shoot/root ratio (S/R) and total leaf area (TLA) were calculated 90 days after spore density counting and root colonization. Infection rates recorded for treatments inoculated with AMFs ranged from 47.95 to 53.55 %. The treatment inoculated with this fungus, without organic fertilizer, presented longer plant length (19.0 cm) than the control (16.6 cm). Inoculation with AMFs was significant for dry weight gain in comparison to the control. Organic fertilization also affected plant's dry weight gain. The highest essential oil content means were observed in treatments with AMFs and manure (0.27 %); this outcome was statistically different from that without AMFs and manure (0.16 %). Based on the PCA analysis, inoculation with AMFs - without/with organic fertilizer - had positive influence on the content of citral (geranial + neral), phenols, and flavonoids in the current study. Accordingly, the use of AMFs and cattle manure has influenced dry weight production, content, and yield, as well as the chemical constituents of the essential oil. According to these findings, the combination of these practices can enhance production in the cultivation of this species, and allow greater dry weight, yield, and active ingredient content. [ABSTRACT FROM AUTHOR]