Antibacterial Activity of Sustainable Thymol Nanoemulsion Formulations Against the Bacterial Blight Disease on Cluster Bean Caused by Xanthomonas axonopodis.

ABSTRACT

The aim of the present study was nanoencapsulation of thymol to improve its poor water solubility and preservation of encapsulated thymol against environmental conditions. Another goal of the current investigation was to assess the antibacterial activity of thymol nanoemulsion as a sustainable biopesticide to control the bacterial blight of cluster bean. An oil-in-water (o/w) nanoemulsion containing thymol was prepared by a high-energy emulsification method using gum acacia and soya lecithin as natural emulsifiers/surfactants. The characterization of thymol nanoemulsion was carried out using dynamic light scattering (DLS), transmission electron microscope (TEM) and Fourier transform infrared spectroscopy (FTIR). A mean particle size of about 83.38 nm was recorded within 10 min of sonication. The stability analysis of optimized nanoemulsion showed kinetic stability up to two months of storage at room temperature. The thymol nanoemulsion was found to be spherical with a size ranging from 80-200 nm in diameter using transmission electron microscopy. Fourier transform infrared spectroscopy was used to study the molecular interaction between emulsifier/surfactant and thymol. The antibacterial studies of thymol nanoemulsion (0.01-0.06%, v/v) by growth inhibition analysis showed a potential antibacterial effect against Xanthomonas axonopodis pv. cyamopsidis (18-0.1 log CFU/ml). Further, in field experiments, foliar spray of the different concentration of thymol nanoemulsion (0.01-0.06%, v/v) significantly increased the percent efficiency of disease control (25.06-94.48%) and reduced the disease intensity (67.33-4.25%) of bacterial blight in cluster bean.