Microbial diseases (caused by bacteria, fungi, viruses, and protozoa) in plants account for about 16% of agricultural yield losses, with fungal pathogens responsible for 70–80% of the total microbial infections. The present study focuses on developing a bio-based oil-in-water (O/W) nanoemulsion formulation for pesticide application. Lemongrass (Cymbopogon flexuosus) essential oil (EO) was incorporated as the active agent, and rhamnolipid (RL) biosurfactant served as the emulsifier. RL exhibited more than 50% emulsification activity in all tested hydrophobic substrates and, at 1 g/L, it demonstrated a lower surface tension value (30.15 mN/m) than its synthetic counterpart, sodium dodecyl sulfate (SDS) (32.87 mN/m). Lemongrass EO exhibited a minimum inhibitory concentration MIC of 3.2 mg/mL against Rigidoporus microporus and Fusarium oxysporum, and 4.0 mg/mL against Ganoderma boninense, with minimum fungicidal concentration (MFC) ranging from 3.2 to 4 mg/mL. Nanoemulsions stabilized with RL were prepared at varying oil-to-surfactant ratios (OSR) using ultrasonication. The optimized formulation (A2) was prepared at an OSR of 1:2, corresponding to 10% oil (v/v) of the total emulsion volume. Formulation A2 exhibited a mean particle size of 119.95 nm with a polydispersity index (PDI) of 0.35. The formulation also showed favourable physicochemical properties, including a zeta potential of − 27.63 mV, viscosity of 22.56 mPa/s, and surface tension of 23.9 mN/m, along with good storage stability. The sonication time was optimized to 10 min to achieve minimal droplet size and PDI. Overall, this study demonstrates that RL-stabilized lemongrass EO nanoemulsions can serve as an eco-friendly nanofungicide, offering a sustainable alternative to synthetic fungicides in managing fungal phytopathogens.   Keywords: Nanoemulsion, lemongrass, Pseudomonas-derived rhamnolipids

Figure 1: Emulsification activity of RLs, SDS and distilled water against different hydrophobic substrates after (a) 1 day and (b) 30 days of incubation at room temperature (24 °C)

Figure 2: Surface tension of RLs and SDS at different concentrations

Source: Manemegalai Suria Gandi, Khairulmazmi Ahmad, Mohd Noriznan Mokhtar, Mohd Rafein Zakaria. 2025. Nanoemulsion formulation of lemongrass essential oil using Pseudomonas-derived rhamnolipids for targeted phytopathogen suppression. 3 Biotech 15, 404.

Date of Input: 31/12/2025 | Updated: 31/12/2025 | ainzubaidah