Cell structure damage contributes to antifungal activity of sodium propylparaben against Trichothecium roseum.

Trichothecium roseum is a type of fungus that causes pink rot in muskmelon after the melons are harvested. Pink rot leads to severe decay during storage and causes the production of toxins that can be harmful to human health. Sodium propylparaben (SPP, IUPAC name: sodium; 4-propoxycarbonylphenolate) is an antimicrobial preservative that can be used to treat the inedible parts of fruits in addition to food, medications, and packaging. In this study, the effectiveness of SPP in inhibiting T. roseum was tested, and the inhibition mechanism was investigated. The results show that SPP inhibited the growth and spore germination of T. roseum. The malondialdehyde (MDA) content, propidium iodide staining, alkaline phosphatase (AKP) activity, and calcofluor white (CFW) staining results show that SPP produced a disruption of the cell membrane and cell wall integrity of T. roseum. Scanning and transmission electron microscopy (SEM and TEM, respectively) results also indicate that SPP disrupted the cellular structure of T. roseum. Meanwhile, the large amounts of superoxide anion and hydrogen peroxide in T. roseum accumulated due to the effects of SPP on the activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, superoxide dismutase, and decreased catalase. In addition, SPP caused a significant reduction in the incidence rate and disease degree of muskmelon pink rot in vivo. In conclusion, SPP appears to be effective against T. roseum via disruption of the cell membrane and wall. SPP could be used to manage melon pink rot after fruit harvesting because of its disease inhibition effect in vivo.

Inhibitory Effect and Mechanism of Carvacrol against Black Mold Disease Agent Alternaria alternata in Goji Berries.

Alternaria alternata, as a main decay fungus of goji berry, can produce mycotoxins such as alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TeA). Carvacrol (CVR) has exhibited a broad-spectrum antifungal activity in vitro. We assumed that CVR can also be applied to control Alternaria rot on goji berries and mycotoxins produced by the pathogens. To investigate whether CVR impacts the accumulation of mycotoxins and cell membrane damage of A. alternata, the antifungal activity of CVR on the fungal growth and mycotoxin production was evaluated in this study. The results showed that the minimum inhibitory concentration (MIC) of CVR against A. alternata was 0.12 µL/mL. Meanwhile, the destruction of plasma membrane integrity, cytoplasmic leakage, intracellular oxidative damage, and inhibitory effect in vivo were also observed in A. alternata treated with CVR. Moreover, CVR significantly reduced the accumulation of AOH, AME, and TeA. Transcriptomic profiling was performed by means of comparative RNA-Seq analysis to research the gene expression level of A. alternata, which attested to significant changes in nitrogen metabolism, carbon utilization, fatty acid oxidation, and antioxidant enzymes in CVR-treated A. alternata. This study suggests a new understanding of the molecular mechanism of response to CVR treatment in A. alternata, indicating that CVR is a novel antifungal agent with the potential to be applied to various fungi.

Inhibitory effect of carvacrol against Alternaria alternata causing goji fruit rot by disrupting the integrity and composition of cell wall.

Goji (Lycium barbarum L.) is a widely planted crop in China that is easily infected by the pathogenic fungus Alternaria alternata, which causes rot after harvest. Previous studies showed that carvacrol (CVR) significantly inhibited the mycelial growth of A. alternata in vitro and reduced Alternaria rot in goji fruits in vivo. The present study aimed to explore the antifungal mechanism of CVR against A. alternata. Optical microscopy and calcofluor white (CFW) fluorescence observations showed that CVR affected the cell wall of A. alternata. CVR treatment affected the integrity of the cell wall and the content of substances in the cell wall as measured by alkaline phosphatase (AKP) activity, Fourier transform-infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Chitin and ß-1,3-glucan contents in cells decreased after CVR treatment, and the activities of ß-glucan synthase and chitin synthase decreased. Transcriptome analysis revealed that CVR treatment affected cell wall-related genes in A. alternata, thereby affecting cell wall growth. Cell wall resistance also decreased with CVR treatment. Collectively, these results suggest that CVR may exert antifungal activity by interfering with cell wall construction, leading to impairment of cell wall permeability and integrity.

Metabolic Profiling and Molecular Mechanisms Underlying Melatonin-Induced Secondary Metabolism of Postharvest Goji Berry (Lycium barbarum L.).

Postharvest decay of goji berries, mainly caused by Alternaria alternata, results in significant economic losses. To investigate the effects of melatonin (MLT) on resistance to Alternaria rot in goji berries, the fruits were immersed in the MLT solutions with varying concentrations (0, 25, 50, and 75 µmol L-1) and then inoculated with A. alternata. The results showed that the fruits treated with 50 µmol L-1 MLT exhibited the lowest disease incidence and least lesion diameter. Meanwhile, endogenous MLT in the fruits treated with 50 µmol L-1 MLT showed higher levels than in the control fruits during storage at 4 ± 0.5 °C. Further, the enzymatic activities and expressions of genes encoding peroxidase, phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, 4-coumarate-CoA ligase, chalcone synthase, chalcone isomerase, and cinnamyl alcohol dehydrogenase were induced in the treated fruit during storage. UPLC-ESI-MS/MS revealed that secondary metabolites in the fruits on day 0, in order of highest to lowest levels, were rutin, p-coumaric acid, chlorogenic acid, ferulic acid, caffeic acid, naringenin, quercetin, kaempferol, and protocatechuic acid. MLT-treated fruits exhibited higher levels of secondary metabolites than the control. In conclusion, MLT treatment contributed to controlling the postharvest decay of goji fruit during storage by boosting endogenous MLT levels, thus activating the antioxidant system and secondary metabolism.

Chemical Composition, Crystal Morphology, and Key Gene Expression of the Cuticular Waxes of Goji (Lycium barbarum L.) Berries.

The cuticular wax of fruit is closely related to quality, storability, and pathogen susceptibility after harvest. However, little is known about the cuticular wax of goji berry (Lycium barbarum L.) cultivars. In the present study, the chemical composition, crystal structures, and expression levels of associated genes of the cuticular wax of six goji cultivars were investigated. We detected 70 epicuticular wax compounds in six goji cultivars. Among them, fatty acids, alkanes, and primary alcohols were the major components of the cuticular wax of goji berries, which were related to the formation of irregular lamellar crystal structures. The terpenoid compounds in the cuticular wax of goji berries were highly resistant to Alternaria rot. Moreover, the CER1, CER6, LACS1, MAH1, LTP4, ABC11, MYB96, and WIN1 genes in goji berries might be closely related to wax synthesis. These results provide valuable information for breeding and screening goji cultivars suitable for postharvest storage.