Does essential oil microencapsulation provide a sustainable approach to biostimulation in tomato crops?

The application of encapsulation technologies to protect and deliver bioactive compounds, such as essential oils, in a controlled manner is an area of great interest. Essential oils, which are rich in volatile organic compounds (VOCs), have biostimulant potential that affects plant growth and physiology. However, their effects at the molecular level are not well understood. In addition, their instability and volatility limit their direct application. Therefore, this study investigates the development of innovative biostimulant formulations for tomato using the microencapsulation technique to overcome these challenges and improve the efficacy of VOCs present in rosemary (Rosmarinus officinalis), lemon balm (Lippia alba) and orange (Citrus sinensis) essential oils. Colloidal suspensions containing the essential oils were developed using cassava starch (native and modified) as the biopolymer and polysorbate 80 as the surfactant. A factorial design was used to optimize the process variables affecting the recovery of essential oils. The formulations were characterized for viscosity, morphology by scanning electron microscopy (SEM) and thermal stability by thermogravimetric analysis (TGA). Encapsulation efficiency and VOC release profile were evaluated by gas chromatography-mass spectrometry (GC-MS). The optimized formulations were applied to wild (Solanum pimpinellifolium) and commercial (S. lycopersicum) tomato cultivars, and metabolomic analyses by UHPLC-q-ToF-MS/MS and CG-EM were performed to evaluate the effects on plant metabolism. The use of modified cassava starch, combined with the addition of excipients (lignin, banana and pequi residues), optimized the microencapsulation process, achieving VOC recoveries higher than 85% (v v^-1). The biopolymer microcapsules demonstrated improved retention of essential oils in soil and increased thermal stability of the active ingredients. In vitro release assays indicated a controlled release profile of VOCs. Application of the formulations to tomato plants promoted root growth and modulated leaf metabolism. As evidenced by the metabolomic analyses, we verified the induction in the biosynthesis of metabolites related to defense mechanisms for both cultivars after the treatments, such as alpha and beta-tomatine. Thus, the results obtained provide subsidies for the development of controlled delivery systems of biostimulants containing essential oils, contributing to more sustainable agricultural practices.