Nengguo Tao

Anti-fungal activity of Citrus reticulata Blanco essential oil against Penicillium italicum and Penicillium digitatum

The chemical composition of Citrus reticulata Blanco essential oil was analysed using GC/MS. Monoterpene hydrocarbons (C10H16) constituted the majority (88.96%, w/w) of the total oil. The oils dose-dependently inhibited Penicillium italicum and Penicillium digitatum. The anti-fungal activity of the oils against P. italicum was attributed to citronellol, octanal, citral, decanal, nonanal, β-pinene, linalool, and γ-terpinene, whereas anti-fungal activity against P. digitatum is attributed to octanal, decanal, nonanal, limonene, citral, γ-terpinene, linalool, and α-terpineol. The oils altered the hyphal morphology of P. italicum and P. digitatum by causing loss of cytoplasm and distortion of the mycelia. The oils significantly altered extracellular conductivity, the release of cell constituents, and the total lipid content of P. italicum and P. digitatum. The results suggest that C. reticulata Blanco essential oils generate cytotoxicity in P. italicum and P. digitatum by disrupting cell membrane integrity and causing the leakage of cell components.

Citral exerts its antifungal activity against Penicillium digitatum by affecting the mitochondrial morphology and function.

This work investigated the effect of citral on the mitochondrial morphology and function of Penicillium digitatum. Citral at concentrations of 2.0 or 4.0 μL/mL strongly damaged mitochondria of test pathogen by causing the loss of matrix and increase of irregular mitochondria. The deformation extent of the mitochondria of P. digitatum enhanced with increasing concentrations of citral, as evidenced by a decrease in intracellular ATP content and an increase in extracellular ATP content of P. digitatum cells. Oxygen consumption showed that citral resulted in an inhibition in the tricarboxylic acid cycle (TCA) pathway of P. digitatum cells, induced a decrease in activities of citrate synthetase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, succinodehydrogenase and the content of citric acid, while enhancing the activity of malic dehydrogenase in P. digitatum cells. Our present results indicated that citral could damage the mitochondrial membrane permeability and disrupt the TCA pathway of P. digitatum.

Transcriptional profiling analysis of Penicillium digitatum, the causal agent of citrus green mold, unravels an inhibited ergosterol biosynthesis pathway in response to citral.

BackgroundGreen mold caused by Penicillium digitatum is the most damaging postharvest diseases of citrus fruit. Previously, we have observed that citral dose-dependently inhibited the mycelial growth of P. digitatum, with the minimum inhibitory concentration (MIC) of 1.78xa0mg/mL, but the underlying molecular mechanism is barely understood.ResultsIn this study, the transcriptional profiling of the control and 1/2MIC-citral treated P. digitatum mycelia after 30xa0min of exposure were analyzed by RNA-Seq. A total of 6355 genes, including 2322 up-regulated and 4033 down-regulated genes, were found to be responsive to citral. These genes were mapped to 155 KEGG pathways, mainly concerning mRNA surveillance, RNA polymerase, RNA transport, aminoacyl-tRNA biosynthesis, ABC transporter, glycolysis/gluconeogenesis, citrate cycle, oxidative phosphorylation, sulfur metabolism, nitrogen metabolism, inositol phosphate metabolism, fatty acid biosynthesis, unsaturated fatty acids biosynthesis, fatty acid metabolism, and steroid biosynthesis. Particularly, citral exposure affected the expression levels of five ergosterol biosynthetic genes (e.g. ERG7, ERG11, ERG6, ERG3 and ERG5), which corresponds well with the GC-MS results, the reduction in ergosterol content, and accumulation of massive lanosterol. In addition, ERG11, the gene responsible for lanosterol 14α-demethylase, was observed to be the key down-regulated gene in response to citral.ConclusionOur present finding suggests that citral could exhibit its antifungal activity against P. digitatum by the down-regulation of ergosterol biosynthesis.

Effect of applying cinnamaldehyde incorporated in wax on green mould decay in citrus fruits

BACKGROUNDnGreen mould caused by Penicillium digitatum is the most damaging postharvest diseases of citrus fruit. Cinnamaldehyde (CA) is a food additive that has potential use in controlling postharvest disease of fruits and vegetables. In this study, the effectiveness of wax with CA (WCA) in controlling Ponkan (Citrus reticulata Blanco) green mould was investigated.nnnRESULTSnThe mycelial growth of P. digitatum was inhibited by CA in a dose-dependent manner. The minimum inhibitory concentration and minimum fungicidal concentration (MFC) were both 0.50u2009mL L-1 . In vivo tests demonstrated that WCA (1u2009×u2009and 10u2009×u2009MFC) applied to Ponkan fruits inoculated with P. digitatum could significantly decrease the incidence of green mould for up to 5u2009days. The WCA treatment increased the activities of catalase, superoxide dismutase, peroxidase, phenylalanine ammonia lyase, polyphenol oxidase, as well as the total phenols and flavonoids contents. Meanwhile, the treatment remarkably decreased the weight loss rate of fruits and maintained fruit quality. These results indicated that WCA treatment might induce defence responses against green mould in citrus fruit.nnnCONCLUSIONnOur findings suggest that WCA might be a promising approach in controlling green mould of citrus fruits.

Effect of octanal on the mycelial growth of Penicillium italicum and P. digitatum

The present study investigated the antifungal activity of octanal against Penicillium italicum and P. digitatum. Results showed that octanal exhibited strong antifungal activity against the test pathogens in a dose-dependent manner. Scanning electron microscopy observation revealed that octanal obviously altered the morphology of P. italicum and P. digitatum hyphae by causing the loss of cytoplasm and distortion of mycelia. A rapid increase in the membrane permeability of P. italicum and P. digitatum was observed after treated with octanal at minimum inhibitory concentration or minimum fungicidal concentration, evidenced by the release of cell constituents, the extracellular conductivity and the extracellular potential of hydrogen. In addition, octanal apparently induced a decrease in total lipid contents of P. italicum and P. digitatum cells. These results suggested that the antifungal activity of octanal against P. italicum and P. digitatum can be attributed to the disruption of the cell membrane integrity and the leakage of cell components.

A Damaged Oxidative Phosphorylation Mechanism Is Involved in the Antifungal Activity of Citral against Penicillium digitatum

Citral exhibits strong antifungal activity against Penicillium digitatum. In this study, 41 over-expressed and 84 repressed proteins in P. digitatum after 1.0 μL/mL of citral exposure for 30 min were identified by the iTRAQ technique. The proteins were closely related with oxidative phosphorylation, the TCA cycle and RNA transport. The mitochondrial complex I, complex II, complex III, complex IV and complex V, which are involved in oxidative phosphorylation were drastically affected. Among of them, the activities of mitochondrial complex I and complex IV were apparently suppressed, whereas those of mitochondrial complex II, complex III and complex V were significantly induced. Meanwhile, citral apparently triggered a reduction in the intracellular ATP, the mitochondrial membrane potential (MMP) and glutathione content, in contrast to an increase in the glutathione S-transferase activity and the accumulation of reactive oxygen species (ROS). Addition of exogenous cysteine decreased the antifungal activity. In addition, cysteine maintained the basal ROS level, deferred the decrease of MMP and the membrane damage. These results indicate that citral inhibited the growth of P. digitatum by damaging oxidative phosphorylation and cell membranes through the massive accumulation of ROS.

Antifungal mechanism of sodium dehydroacetate against Geotrichum citri-aurantii

This study investigated the potential anti-fungal mechanisms of sodium dehydroacetate (SD) against Geotrichum citri-aurantii. The results showed that the cell wall integrity of G. citri-aurantii was not affected, whereas the membrane permeability of G. citri-aurantii mycelia was visibly altered by SD. Dramatic morphological changes of the mycelia, such as loss of cytoplasm, plasmolysis, and dissolution of intracellular substances, were observed by scanning electron microscopy and transmission electron microscopy analyses, indicating that the mycelium is severely damaged by the SD treatment. Furthermore, SD apparently induced a decrease in the intracellular ATP content before 30xa0min of exposure. An increase in the activity of the Na+/K+-ATPase was also observed, indicating that Na+ ions might enter the cell and thus disturb the energy supply. Taken together, this study’s findings suggest that the anti-fungal activity of SD against G. citri-aurantii can be attributed to the disruption of cell membrane permeability and energy metabolism.