Arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria promoted changes in plant metabolism and the volatile profile of Piper callosum Ruiz & Pav

Piper callosum Ruiz & Pav. is known in the Amazon as a paregoric elixir and exists as a shrub native to the Neotropics. In traditional medicine, the tea from its leaves is used to treat pain in the digestive tract, rheumatism, and muscular aches. This study aimed to evaluate the influence of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) inoculation on the secondary metabolism of P. callosum. The plants were inoculated after 30 days of cultivation and kept in a greenhouse. Plant development parameters were monitored at 30-, 60-, and 90-days after inoculation (DAI) and indicated that AMF and PGPR favored plant growth throughout all stages of development. The leaf volatiles extracted by simultaneous distillation and extraction were analyzed by gas chromatography coupled with mass spectrometry and showed that phenylpropanoids and monoterpene hydrocarbons were predominant in all essential oils, revealing distinct abundance patterns across the different sampling points. The major volatile compounds identified were safrole, methyl eugenol, and β-pinene, and a reduction trend in their content was observed for safrole and methyl eugenol, especially at 90 DAI in both treatments. Principal component analysis revealed that germacrene D-4-ol and limonene were among the most influential in both treatments. Finally, the total phenolic content and the enzymatic activity of phenylalanine ammonia-lyase revealed different effect patterns for inoculation and time of evaluation on each treatment. All the data presented indicate that symbiotic inoculation can optimize the production of essential oil, which can improve the quality and productivity of P. callosum plants.