Chitosan-coated nanoemulsions of a terpene-based natural deep eutectic solvent and lemongrass essential oil to control coffee leaf rust: Two alternatives based on natural products

Abstract

Coffee production is negatively affected by coffee leaf rust, a disease caused by the fungus Hemileia vastatrix. As a natural product-based alternative to chemically control the disease, this study evaluated the effect of two chitosan-coated nanoemulsions prepared from Cymbopogon citratus essential oil (EO) and the thymol: pyruvic acid (1:1) natural deep eutectic solvent (NADES) on the in vitro germination of H. vastatrix urediospores and on the in vivo control of the disease in Coffea arabica plants under greenhouse conditions. Both nanoformulations inhibited urediospores in vitro germination but only that prepared with EO did it significantly more than its free form active ingredient (the observed reduction was around 60 %). On the other hand, the in vivo experiment showed that the EO and NADES chitosan-coated nanoemulsions offered similar and significant protection for Coffea arabica plants against leaf rust; the disease severity level was found to be less than 2.6 % after 81 days from the application of the treatments to the plants (comparable to the cooper oxychloride, which is one of the commercial fungicides traditionally used), while the free components did not (9.0–13.3 % of severity level by day 81, such as the control). This is the first report demonstrating that chitosan-coated nanoemulsions, containing NADES or EO, protect coffee plants against H. vastatrix infection and can be two alternatives for sustainable pest management. Furthermore, this study contributes to broadening the prospects for using hydrophobic NADES in the design of biopesticides.