Sustainable Control of Monilinia laxa in Peach Using a Treatment Based on Eugenol, Thymol, and Geraniol

Abstract

Peach fruit (Prunus persica) is highly susceptible to postharvest decay caused by Monilinia laxa, resulting in significant economic losses. To our knowledge, this is the first study that evaluated the antifungal efficacy of the 3Logy® commercial formulation containing eugenol, thymol, and geraniol against M. laxa both in vitro and in vivo, and assessed its effects on fruit quality, antioxidant metabolism, and defense-related gene expression. In vitro results showed a strong concentration-dependent inhibition of mycelial growth, reaching 82.2% inhibition at 100 µg/mL, the concentration selected for the in vivo experiments, and complete inhibition at the highest concentration tested (250 µg/mL). In vivo, the treatment significantly reduced lesion development (−96%) and disease incidence compared to untreated inoculated fruit. The treatment preserved key physicochemical parameters, including firmness and titratable acidity, while maintaining soluble solids within normal ripening ranges. Additionally, higher levels of phenolic compounds, flavonoids, and antioxidant activity were found in treated fruit. Moreover, enzymatic analyses revealed enhanced activity of antioxidant enzymes (SOD, CAT, and APX), particularly under pathogen stress, indicating activation of the fruit defense system. Gene expression analysis confirmed the upregulation of defense-related genes (CAT, PPO, and PAL), especially in treated and infected samples. Furthermore, the stability of reference genes was validated, highlighting the importance of their selection for accurate RT-qPCR normalization. Overall, these results indicate that the formulation can reduce the severity of brown rot and delay the development of the disease under the experimental conditions tested, while preserving and improving fruit quality.