Fungo micorrízico arbuscular no crescimento e na produção de cumarina em Mikania laevigata Shultz Bip. ex Baker

Abstract

Guaco (Mikania laevigata Shultz Bip. ex Baker) is a medicinal plant traditionally used to treat respiratory diseases such as cough and bronchitis. Its main bioactive compounds include coumarin, chlorogenic and dicaffeoylquinic acids, as well as essential oils containing germacrene D, caryophyllene oxide, and spathulenol. One strategy to enhance the production of these compounds is through soil microbiota management, with arbuscular mycorrhizal fungi (AMF) inoculation being a promising approach to stimulate plant growth and secondary metabolite synthesis in medicinal species. This study evaluated the effects of Rhizophagus clarus inoculation on the growth, coumarin production, and mycorrhizal symbiosis of M. laevigata cultivated under different soil conditions (autoclaved or non-autoclaved). The experiment was conducted in a completely randomized design, in a 2 x 2 factorial scheme, with 10 replicates. The factors evaluated were AMF inoculation (presence of inoculum – CF and absence of inoculum – SF) and soil condition (autoclaved – SA and non-autoclaved – SNA). Morphological variables (height, number of leaves, and shoot, root, and total biomass), coumarin content, mycorrhizal colonization, and spore density were analyzed. The treatment with non-autoclaved and inoculated soil (CFSNA) showed the best results, with a total biomass of 12.95 g, height of 216.2 cm, 71.4 leaves, coumarin content of 0.83 mg, 91.4% mycorrhizal colonization, and 212.5 spores/50 g of soil. In contrast, the treatment with autoclaved soil and no inoculation (SFSA) presented the lowest values for all variables. The coumarin content observed in CFSNA represented a 20.59% increase compared to SFSA, exceeding the minimum value established by the Brazilian Pharmacopoeia (6th edition), which requires at least 0.15% coumarin in dried M. laevigata leaves. The results demonstrate that the simultaneous presence of R. clarus and native soil microbiota enhances mycorrhizal symbiosis, promoting plant growth and intensifying the biosynthesis of coumarin, the main bioactive compound of M. laevigata. The significant increase in coumarin content reinforces the role of AMF in optimizing the plant’s secondary metabolism. Thus, the use of R. clarus represents an effective strategy for cultivating M. laevigata with greater productivity, higher coumarin levels, and improved pharmacological quality.