Farnesol nanoemulsions modulate growth and metabolism under Fusarium oxysporum exposure, and defense gene expression in lettuce

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 PERMANOVA 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. • Farnesol application in lettuce increases dry weight under F. oxysporum exposure. • Less fructose, aminoacids, and minerals were synthesised with farnesol treatments. • Farnesol at 0.3% dose upregulated LsLOX2, LsNPR1, LsGPX8 and LsCAT1 genes. • A dose dependent shift from defense induction to represion was produced by farnesol at 0.7% in lettuce plants.