Abstract

Farnesol, a naturally occurring sesquiterpenoid alcohol, has emerged as a promising bioactive volatile for sustainable crop protection. This study evaluated the efficacy of farnesol nanoemulsions as potential plant defense elicitors against Fusarium oxysporum f. sp. lactucae in lettuce (Lactuca sativa). Two susceptible varieties (Berruguete and Signas) were sprayed with two doses of farnesol (0.3% and 0.7%) or controls, with and without subsequent fungal inoculation. The effects on plant growth, metabolic profile, disease incidence, and the expression of key defense-related genes were evaluated. The nanoemulsions exhibited good colloidal stability over time (34 days) with particle sizes of 75-104 nm and Z-potential values between-3.66 to-27.6 mV. In inoculated plants, the 0.3% dose enhanced dry weight in comparison with the control and the 0.7% treatment. Metabolic profiling revealed alterations in carbohydrate metabolism, particularly fructose levels, in response to both pathogen exposure and farnesol treatment, with a statistically significant interaction [F(2,53)= 6.55**]. No clear external wilt symptoms were observed during the experimental period; however, F. oxysporum was isolated from collar tissues in a proportion of plants, indicating that colonization was not prevented. The low 0.3% farnesol dose, triggered an upregulation of genes from the JA (LsLOX2 and LsMYC2), SA (LsNPR1) or ROS scavenging (LsCAT1 and LsGPX8) pathways, in Berruguete variety, although a strong repression was produced with the high 0.7% dose. Two principal components explained 58% or 74.5% of variability in growth and chemical composition or gene expression profile parameters, respectively. A very highly significant PERMA-NOVA was obtained for the effects of farnesol treatment [F(2,29)= 6.32***] in the multivariate analysis with absence of fungus exposure data. The results indicate that farnesol might acts as an elicitor in lettuce. There was a dose-dependent hormetic response and this is an important issue for practical application of this natural product on agricultural crops.