Dissipation of emamectin benzoate in okra and its residual impact on okra metabolome

Abstract

Pesticide absorption is a complex process in which pesticides undergo transformation and affect plant metabolic processes and hence investigated the metabolic fate of emamectin benzoate, a macrocyclic lactone insecticide. Residues of emamectin benzoate followed first order kinetics in field with pre-harvest intervals of 1.96 and 2.54 days respectively, at single and double dose of applications. Both in leaves and fruits of okra, the emamectin benzoate metabolites, emamectin B1a1 and emamectin B1b1 accumulated up to third day and the metabolite 4'’-deoxy-4'’-epi-N-methylaminoavermectin-b1-benzoate was detected only in fruits and was absent in okra leaves. A comprehensive evaluation of metabolic variations in okra induced by emamectin benzoate compared to the unsprayed plant samples was conducted by UHPLC-ESI-Q-Orbitrap high-resolution mass spectrometer (HRMS) and data analysed by compound discoverer 3.3. The metabolomic results suggested that emamectin benzoate could affect the plants defence mechanism, and a total of 818 metabolites including organic acids, amino acids, phenolics, flavonoids and fatty acids, were clearly altered. The content of defence-related L-proline and other proline related compounds were significantly increased by emamectin benzoate. Many phenolics and flavonoids, such as hyperoside and quercetin, were significantly accumulated, which could benefit the plant to alleviate the stress conditions due to the application of insecticide.