Avaliação in vitro de óleos essenciais como uma alternativa biotecnológica no controle do cancro cítrico

Abstract

In recent years, the incidence of citrus canker in Brazilian citrus-growing regions has increased significantly, a phenomenon aggravated by the change in São Paulo state legislation in 2017, which allowed the maintenance of symptomatic plants in orchards and further intensified the spread of the disease, reinforcing the urgent need for biotechnological alternatives for its control. In this context, this study investigated the antimicrobial potential of eleven essential oils (EOs) – Pinus sylvestris, Zingiber officinale, Foeniculum vulgare, Citrus aurantium amara, Rosmarinus officinalis, Citrus sinensis, Cinnamomum cassia, Eugenia caryophyllus, Ocimum basilicum, Melaleuca alternifolia, and Thymus vulgaris – through microdilution assays for the determination of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and chemical profiling by Gas Chromatography–Mass Spectrometry (GC–MS). The six EOs that exhibited the lowest MBC values were used to compose binary mixtures (50:50), in which antimicrobial parameters and interaction profiles (synergistic, additive, indifferent, or antagonistic) were evaluated. Additive effects were observed for the formulations of T. vulgaris and P. sylvestris and O. basilicum with M. alternifolia. For the binary combinations that showed the greatest antibacterial activity, additional mixtures were prepared at 80:20 and 20:80 ratios. The formulations at different proportions revealed higher antimicrobial efficacy for C. cassia and M. alternifolia and C. cassia with O. basilicum, both at the 80:20 ratio, which presented the lowest MBC values. The most promising mixtures were chemically characterized by GC–MS, and activity data were correlated with the profiles using chemometric analyses by Partial Least Squares regression (PLS and VIP scores), allowing the identification of compounds most relevant to antibacterial activity, in this case cinnamaldehyde, eugenol, and L-4-terpineol. The EOs were also analyzed for their antioxidant potential and phenolic compound content. The evaluation of the antioxidant activity of the isolated EOs sought to establish possible correlations between antioxidant properties and antimicrobial effects, providing evidence of the potential of these bioactive compounds as innovative biocontrol strategies against Xanthomonas citri subsp. citri.