Essential Oils Reduce Grey Mould Rot of Apples and Modify the Fruit Microbiome during Postharvest Storage

Abstract

Botrytis cinerea is the causal agent of grey mould rot of apples. The efficacy of biofumigation with thyme (Thymus vulgaris), savoury (Satureja montana), and basil (Ocimum basilicum) essential oils (EOs) at 1%, 0.5%, and 0.1% concentrations were tested against B. cinerea. In vitro, the results showed 100% growth inhibition at 1% concentration for all oils. Subsequent biofumigation experiments on apples of cultivar ‘Opal’ with 1% EOs showed that, after 60 d storage, thyme and savoury EOs significantly reduced grey mould rot incidence (average incidence 2% for both treatments) compared to the control (7%). Analyses of quality indicated slightly higher fruit firmness for 1% thyme at 30 d and slightly higher titratable acidity for 1% thyme and savoury at 60 d. Sampling of the atmosphere inside the cabinets was performed to characterize and quantify the volatile components of EOs released through biofumigation. Though thymol and p-cymene were the main components of thyme EO, the antimicrobial activity was mainly due to the presence of thymol and, to a lower extent, of carvacrol. In savoury EO, carvacrol and p-cymene were the main components, whereas in basil EO, linalool and estragole were mainly present. Metabarcoding analyses showed that the epiphytic microbiome had higher richness and evenness compared to their endophytic counterpart. By the end of shelf-life, treatments with thyme EO reduced B. cinerea abundance compared to the inoculated control for both endophytes (from 36.5% to 1.5%) and epiphytes (from 7.0% to 0.7%), while favouring a significant increase in Penicillium species both in endophytes (from 0.2% to 21.5%) and epiphytes (from 0.5% to 18.6%). Results indicate that thyme EO (1%) and savoury EO (1%) are equally effective in hampering grey mould rot development in vivo.

Efficacy of Essential Oil Vapours in Reducing Postharvest Rots and Effect on the Fruit Mycobiome of Nectarines

“…Five biological replicates consisting of 15 nectarines were analyzed at each time point for each treatment. Microbiome sampling and genomic DNA extraction were performed as described in Schiavon et al [16]. For epiphyte sampling, the surface of each nectarine was rubbed with sterile cotton swabs dipped in sterile phosphate-buffered saline (PBS) solution.…”

“…They are popular for their wide range of applications, including aromatherapy, personal care products, natural cleaning agents, and even culinary purposes [10][11][12]. Moreover, their antimicrobial and antioxidant properties [13,14] make them attractive for preserving the quality and extending the shelf life of fruits and vegetables [3,15,16]. EOs are extracted from various plant parts, including flowers, leaves, bark, stems, and roots [17].…”

“…The use of these substances in managing postharvest diseases, however, is hampered by phytotoxicity phenomena even at moderate concentrations [30]. A possible solution is the application of EOs through biofumigation, in which they are released slowly into the storage atmosphere through diffusers, avoiding direct contact with the fruits [16,33,38].…”

Biotechnological and Biocontrol Approaches for Mitigating Postharvest Diseases Caused by Fungal Pathogens and Their Mycotoxins in Fruits: A Review

“…Essential oils derived from various plant sources possess antimicrobial properties and have been explored for postharvest disease control . Numerous essential oils are discovered for the antifungal properties of gray and brown molds in strawberries, peaches, pears, and plums. − For example, essential oils such as oregano oil, thyme oil, and cinnamon oil have exhibited antifungal activity against pathogens such as P. expansum , , B. cinerea , , Fusarium spp., and Alternaria spp …”

“…80 Numerous essential oils are discovered for the antifungal properties of gray and brown molds in strawberries, peaches, pears, and plums. 81−83 For example, essential oils such as oregano oil, thyme oil, and cinnamon oil have exhibited antifungal activity against pathogens such as P. expansum, 84,85 B. cinerea, 86,87 Fusarium spp., and Alternaria spp. 88 Another notable biochemical in fruit postharvest pathology is salicylic acid (SA).…”