Potencial dos compostos orgânicos voláteis como estimulantes vegetais: uma investigação em diferentes cultivares de tomate

Abstract

Essential oils extracted from plants are composed of volatile organic compounds that have a wide range of biological activities in vital systems. Various effects of essential oils on plant growth have been demonstrated. However, their effects at the molecular level are not well understood. In addition, their volatile and degradable nature limits their application. Therefore, we investigated the potential of rosemary (Rosmarinus officinalis), lemon balm (Lippia alba), and orange (Citrus sinensis) essential oils as plant biostimulants using the tomato cultivars Solanum pimpinellifolium and S. lycopersicum as models, classified as Plant Introduction (PI) and commercial, respectively. To evaluate the biostimulant activity of essential oils, this study was conducted in three research fronts, namely (i) the development of the formulation containing the biostimulant, (ii) the evaluation of extraction methods to characterize biotic interactions, and (iii) the application of the formulated products in tomato cultivars. The first stage of the research was to improve the dispersion of essential oils in an aqueous medium. Therefore, a method for obtaining biopolymer microcapsules containing essential oils was evaluated. To prepare the microcapsules, we evaluated the type of biopolymer (native and modified manioc starch), the surfactant content (polysorbate 80) and the addition (or not) of adjuvants (banana, pequi and lignin residues). The emulsions were analyzed for their viscosities, surface morphologies, and oil concentrations after emulsion preparation and soil application. We found that the use of modified starch combined with the addition of adjuvants favored the microencapsulation process with essential oil recoveries higher than 85% (v v-1). In the soil tests, we observed that the biopolymer microcapsules allowed the retention of oils twice as high as the emulsified oils. For the second phase of this study, we investigated the extraction techniques of plant samples for instrumental metabolomic analysis. This process was essential to ensure standardization and reproducibility of plant material analyses. Using the methods evaluated, we observed that for both cultivars there was a gradual modulation of gibberellins and furanocoumarin precursors during the developmental stages. In addition, commercial plants showed a higher accumulation of isoflavones in the vegetative stage, which may be related to the purple color of their leaves. The PI during development showed a greater induction in the biosynthesis of glycosylated molecules of quercetin and kaempferol. The PI variety was also the only one in which we detected the beta-tomatine molecule in the developmental stages. In the third step, we applied the formulations containing the essential oils and verified, using standardized methods, the induction in the biosynthesis of metabolites related to defense mechanisms for both cultivars after the treatments. In addition, we confirmed that the essential oils stimulated root growth, confirming their biostimulant potential for tomato plants. These data represent the first step in the development of products containing essential oils as plant biostimulants.