Avaliação do perfil químico do óleo essencial de populações espontâneas de Tagetes minuta L. (Asteraceae) na região sul do Rio Grande do Sul

Abstract

Tagetes minuta L. is a bioactive plant of spontaneous occurrence in the South of Brazil, known to family farmers as an invasive species and frequently used as an insect repellent. However, it can become a new income alternative since its essential oil has properties of interest in the pharmaceutical, cosmetic, food and agricultural bioproducts industry. The aim of this work was to characterize the essential oil of spontaneous populations of T. minuta in municipalities of southern of the Rio Grande do Sul State, trying to identify the occurrence of chemotypes and variability factors in their composition. Plants of six populations of T. minuta were collected between April and May 2015, in the full flowering. The essential oil was extracted from flowers and leaves with petioles by steam-drag and analyzed by GC-MS/GC-FID. Fifteen compounds were identified, and all the populations had the same major compounds, cis-tagetone, cis-β-ocimene, dihydrotagetone, trans-tagetone and limonene, which on average represented 96% of the oil composition. The populations are of the same chemotype. Variations in the proportion of the major compounds allowed grouping the populations into three groups, the first with three samples and 96% similarity, the second with two samples and 86% similarity, and the last sample isolated, with 74% and 79% of similarity with the two previous ones respectively. The first populations harvested had higher levels of dihydrotagetone and limonene whereas those harvested later had higher levels of cis-tagetone and cis-β-ocimene. The date of harvest was a determinant factor in the proportion between the major compounds and presented a negative correlation with the mean air temperature. The occurrence of high rainfall in the days prior to harvest may have interfered in the oil composition of at least one population. The solar radiation had a positive correlation with the contents of cis-tagetone and cisβ-ocimene and negative with dihydrotagetone and limonene. Finally, the essential oil is similar among the different populations of T. minuta evaluated and tends to present a uniform composition of the major compounds, with variations in their proportions due to the phenological stage at the time of harvest.