In vitro/ex vivo fungicide potential of submicron-emulsions prepared from some essential oils of promising plants from colombian Caribbean Region against colletotrichum gloeosporioides and fusarium oxysporum, main damage-causing phytopathogens in yam crops (Dioscorea spp.) in the department of Sucre

Abstract

Yam (Dioscorea spp.) is a key crop of considerable economic and nutritional importance in the rural areas of the Colombian Caribbean, where it provides both a source of food and an alternative livelihood for smalland medium-scale farmers. In 2020, Colombia produced over 420000 tons of yam, of which more than 90% originated from the departments of Bolívar, Córdoba, and Sucre, while ca. 11500 tons were exported to the United States, Central America, the Caribbean, and Europe. Despite its economic significance, yam production in this region has experienced a yield decline of ca. 7.3%, driven by limitations in agronomic practices, adverse weather, restricted access to inputs, and increasing phytosanitary pressures. Among the main constraints are diseases caused by phytopathogenic fungi such as Fusarium oxysporum and Colletotrichum gloeosporioides, responsible for vascular wilt, tuber rot, and anthracnose, which compromise plant physiology, reduce tuber yield and quality, and impose substantial economic burdens on farmers. Traditional disease management relies heavily on synthetic fungicides, particularly benomyl, a broad-spectrum benzimidazole-carbamate fungicide. While effective, benomyl presents significant environmental and health concerns, including aquatic toxicity, soil biota disruption, and potential neurotoxic effects in humans, highlighting the urgent need for safer, sustainable alternatives. In this context, plants and their secondary metabolites [e.g., essential oils (EOs)] emerge as a promising resource for the phytopathogen control (e.g., F. oxysporum and C. gloeosporioides) due to their proven biological potential. Thus, Colombia, being a country with a wealth of plant biodiversity, would offer an abundant source of secondary metabolites (phenols, terpenoids, etc.), many of which have demonstrated potent antifungal activity. Despite these advantages, direct application of EOs in field conditions is often limited by their hydrophobicity, chemical instability, and high volatility, which reduce their bioavailability and efficacy. Advances in formulation technologies (encapsulation and emulsification), particularly at submicron levels, offer a solution to these limitations. For example, emulsions, such as colloidal systems, can be prepared as nano- or mini-emulsions, with droplet sizes ranging from a few nanometers to several hundred nanometers, using high- or low-energy techniques, including ultrasonication. These formulations enhance EO solubility in water, improve chemical stability, and increase biological activity, enabling more effective field application. In addition, the incorporation of other components into the emulsions such as mediumchain triglycerides (MCTs), can prevent destabilizing phenomena like Ostwald ripening and coalescence, prolonging the functional lifespan of EO emulsions while probably maintaining antifungal effectiveness at the same time. This doctorate research focused on the in vitro and/or ex vivo antifungal potential of EOs and their submicron emulsions against F. oxysporum and/or C. gloeosporioides isolated from yam tubers, with the aim to provide a sustainable alternative for the management of fungal disease in yam crops. The study encompassed: (i) chemical characterization of EOs via GC-FID/MS; (ii) evaluation of in vitro antifungal activity through disk diffusion and broth microdilution assays; (iii) optimization and preparation of submicron-emulsions, with or without MCT, using response surface methodology; (iv) assessment of cytotoxicity on human erythrocytes; (v) multivariate statistical analysis to correlate chemical composition and biological activity; and (vi) ex vivo validation on yam tubers for some emulsions. By integrating natural product chemistry, advanced formulation techniques, and rigorous biological assessment, this work seeks to develop environmentally safe, effective, and practical strategies to mitigate fungal diseases in yam, supporting both agricultural productivity and ecological sustainability.