Inhibitory effect and underlying mechanism of cinnamon and clove essential oils on Botryosphaeria dothidea and Colletotrichum gloeosporioides causing rots in postharvest bagging-free apple fruits

Transcription Factor PdTP1 Regulates the Biotransformation of Limonene to α-Terpineol and the Growth of Penicillium digitatum

α-Terpineol, an alcoholic monoterpene with lilac-like aroma, possesses diverse biological activities and has found applications in the food, pharmaceutical, cosmetic, and agricultural industries. Our previous studies indicated that gene PdTP1 was highly expressed in Penicillium digitatum DSM 62840 during the biotransformation of limonene to α-terpineol, while its actual biological functions are not fully understood. Here, PdTP1 was functionally characterized with bioinformatics analysis, subcellular localization, transcriptional activation activity, overexpression, and RNA interference (RNAi) silencing and RNA-seq analysis. Results showed that PdTP1 protein contained a GAL4-like Zn2Cys6 DNA-binding domain and a fungal_trans domain, was located in the nucleus and cell membrane and presented transcriptional activation effect, suggesting that PdTP1 encoded a Zn2Cys6 type transcription factor. Overexpression of PdTP1 in P. digitatum promoted limonene biotransformation and increased α-terpineol production, and opposite results were observed after the silencing of PdTP1. Moreover, transcription factor PdTP1 was found to affect the growth of P. digitatum and participate in ionic stress and oxidative stress responses. RNA-seq data revealed that altering the PdTP1 expression influenced the expression of some genes related to terpene metabolism or biosynthesis, fungal growth, and stress responses. In summary, PdTP1, which encoded a Zn2Cys6 transcription factor, played important roles in improving the production of α-terpineol from limonene and regulating fungal growth and environmental stress responses.

Antifungal Mechanism of Ruta graveolens Essential Oil: A Colombian Traditional Alternative against Anthracnose Caused by Colletotrichum gloeosporioides

Here, we report for the first time on the mechanisms of action of the essential oil of Ruta graveolens (REO) against the plant pathogen Colletotrichum gloeosporioides. In particular, the presence of REO drastically affected the morphology of hyphae by inducing changes in the cytoplasmic membrane, such as depolarization and changes in the fatty acid profile where straight-chain fatty acids (SCFAs) increased by up to 92.1%. In addition, REO induced changes in fungal metabolism and triggered apoptosis-like responses to cell death, such as DNA fragmentation and the accumulation of reactive oxygen species (ROS). The production of essential enzymes involved in fungal metabolism, such as acid phosphatase, β-galactosidase, β-glucosidase, and N-acetyl-β-glucosaminidase, was significantly reduced in the presence of REO. In addition, C. gloeosporioides activated naphthol-As-BI phosphohydrolase as a mechanism of response to REO stress. The data obtained here have shown that the essential oil of Ruta graveolens has a strong antifungal effect on C. gloeosporioides. Therefore, it has the potential to be used as a surface disinfectant and as a viable replacement for fungicides commonly used to treat anthracnose in the postharvest testing phase.

Phytochemical characterization of forest leaves extracts and application to control apple postharvest diseases

The study investigated the antifungal and phytochemical properties of three forest plants (Eucalyptus globulus, Pistacia lentiscus, and Juniperus phoenicea) against apple diseases caused by Colletotrichum gloeosporioides and Alternaria alternata. The determination of the total polyphenol and flavonoid contents in the three aqueous extracts of studied plants showed that E. globulus exhibited the highest contents than those of P. lentiscus and J. phoenicea. Furthermore, the three studied extracts showed very appreciable antioxidant activity with decreasing order: E. globulus, P. lentiscus, and J. phoenicea. The phytochemical analysis showed different common phenolic acids in the three studied plants namely: quinic acid, gallic acid, chlorogenic acid, and caffeoylquinic acid as well as other flavonoids mainly quercetin and catechin. The results of the current study demonstrated that the fungistatic activity of E. globulus EO (4 and 2 µl/ml) seemed to be the most effective under laboratory conditions with an inhibition zone diameter above 16 mm. However, the poisoned food technique indicated that the aqueous extract (80%) and the essential oil (4 µl/ml) of E. globulus exhibited the highest mycelial growth (> 67%) and spore germination (> 99%) inhibition. Preventive treatments with essential oils (4 µl/ml) and aqueous extracts (80%) applied to apple fruits inoculated with A. alternata and C. gloeosporioides resulted in the lowest lesion diameter (< 6.80 mm) and disease severity index (< 15%) and the most favorable inhibitory growth (> 85.45%) and protective potentials (> 84.92%). The results suggest that E. globulus has a brilliant future in the management of anthracnose and Alternaria rot of apple and provide a basis for further studies on its effects under field conditions.

Application of a Chitosan-Cinnamon Essential Oil Composite Coating in Inhibiting Postharvest Apple Diseases

The purpose of this study was to explore the film-forming properties of cinnamon essential oil (CEO) and chitosan (CS) and the effect of their composite coating on postharvest apple diseases. The results demonstrated that the composite coating exhibits favorable film-forming properties at CEO concentrations below 4% (v/v). The effectiveness of the composite coating in disease control can be attributed to two factors: the direct inhibitory activity of CEO against pathogens in vitro and the induced resistance triggered by CS on the fruits. Importantly, the incorporation of CEO did not interfere with the induction of resistance by CS in harvested apples. However, it is noteworthy that the inhibitory effect of the CS-CEO composite coating on apple diseases diminished over time. Therefore, a key aspect of enhancing the preservation ability of fruits is improving the controlled release properties of CEO within CS coatings. This will enable a sustained and prolonged antimicrobial effect, thereby bolstering the fruit preservation capabilities of the composite coatings.