Ontogenetic and Seasonal Variations in Corymbia citriodora Essential Oils: A Study of Chemodiversity and Antifungal Effects Against Botryosphaeria dothidea

Objective As the first of its kind, this research investigates the influence of ontogeny and seasonality on yield and composition of essential oils (EOs) from Corymbia citriodora grown in a homogeneous setting, offering new perspectives on their chemodiversity and antifungal properties against Botryosphaeria dothidea . Methods Leaves of C. citriodora from different seasons and leaf stages were hydro-distilled to extract EOs. Chemical analysis of EOs was done using GC-MS and GC-FID. The EOs from the fresh leaves (FL) and abscission leaves (AL) were tested for their antifungal activity using the microatmosphere method against B. dothidea . Results EO yield varied seasonally in FL, being higher in summer (1.8-2.25% w/w) compared to winter (1.0-1.75% w/w) and significantly lower (0.8-0.82% w/w) in AL. EO from FL was transparent and had a strong lemon fragrance. Whereas EO from AL was pale yellow color and weak aroma. The refractive index (RIs) values of EOs ranges from 1.405 to 1.539. Citronellal was a dominant compound (50.35-82.01%), and it higher levels found in FL. Seasonal and ontogenetic variations influenced the EO composition. Citronellol content (1.10% seasonally, 1.50% across leaf types) and isopulegol content (2.55% seasonally, 2.70% across leaf types) remained relatively less varied across the seasons and developmental stages. Fresh leaf EOs showed strong antifungal activity against B. dothidea , with 100% inhibition at all concentrations (15 µL, 30 µL and 60 µL). However, abscission leaf EOs showed partial inhibition (5.6%) at 15 µL and complete growth inhibition was observed at 30 and 60 µL. Conclusion Essential oil yield was influenced by leaf type and season. Fresh summer leaves producing citronellal-rich oils which showed highest antifungal activity. Notably, the strong antifungal activity of EO from fresh leaves of C. citriodora further reinforces its potential as natural antifungal agents against B. dothidea .