A Evaluation of Lavandula angustifolia Essential Oil as a Postharvest Fungicide Alternative against Penicillium digitatum on Citrus

Abstract

Penicillium digitatum (Pers.) Sacc., the causal agent of green mould, is responsible for approximately 90% of postharvest fungal losses in citrus, which collectively amount to roughly 22.5% of global annual citrus yield. The standard management strategy relies on postharvest application of the synthetic fungicide imidazole; however, the emergence of imidazole-resistant P. digitatum isolates and the fungicide's documented mammalian toxicity necessitate the identification of safer, biodegradable alternatives. This study evaluated the antifungal efficacy of Lavandula angustifolia (lavender) essential oil against P. digitatum under both in vitro and in vivo conditions. Three sequential in vitro experiments were conducted, in which P. digitatum isolates were plated onto potato dextrose agar (PDA) amended with lavender oil concentrations of 0–3200 ppm, 5 ppm imidazole (positive control), and 2000 ppm of a commercially registered clove oil-based product. An in vivo experiment was subsequently performed using Eureka lemons artificially inoculated with two P. digitatum isolates representing contrasting fungicide sensitivity profiles, and treated by dipping in lavender oil solutions (1600, 3200, and 6400 ppm), imidazole, or clove oil. Percentage inhibition (%Inhib) data were statistically analysed using ANOVA and Student's t-test at a 95% confidence level. Results consistently demonstrated a concentration-dependent increase in inhibition, with 3200 ppm lavender oil achieving the highest in vitro efficacy. In vivo, the 3200 ppm concentration outperformed even the 6400 ppm treatment, with inhibition values of 70.7–91.5% for isolate GM 250 and 8.8–62.6% for the less sensitive isolate GM 263. Phytotoxic rind damage was observed at high lavender oil concentrations—an effect attributed to the use of unformulated oil. Although lavender oil demonstrates measurable antifungal potential against P. digitatum, its current limitations in cost, concentration requirement, and phytotoxicity indicate that further formulation development is required before commercial application can be considered. These findings contribute foundational data for the development of essential oil-based, environmentally sustainable citrus postharvest disease management strategies