Yang Bi

A method of analysis for T-2 toxin and neosolaniol by UPLC-MS/MS in apple fruit inoculated with Trichothecium roseum

Trichothecenes are one of the most important groups of mycotoxins produced by Trichothecium roseum, which causes core rot of apple. A reliable and sensitive method was developed and successfully applied for the rapid detection of trichothecenes including T-2 toxin and neosolaniol in harvested apple using UPLC-MS/MS. After the extraction of the two mycotoxins from the apple matrix with methanol/water (80/20, v/v), the concentrated extracts were cleaned-up by PriboFast M270 columns and then analysed by UPLC-MS/MS. T-2 toxin and neosolaniol were effectively separated as unique peaks. The validity of this method was established by its linearity (R2 ≥ 0.9995), precision (relative standard deviation ≤ 3.6%), accuracy, selectivity, limit of detection of 2–5 μg kg–1, limit of quantification of 5–10 μg kg–1 and average recovery of 73–96%. Levels of T-2 toxin were found in the range 7.1–128.4 µg kg–1 in the core rot lesion of three cultivars apple (cvs. Red Delicious, Fuji and Ralls). T-2 was detected not only in the lesion, but also in the tissue without any disease symptoms. However, neosolaniol was only detected in the lesion on ‘Red Delicious’ apples. In addition, the concentration of T-2 toxin in the susceptible cultivar (cv. Fuji) was significantly higher than that in the resistant one (cv. Ralls). This method proved to be suitable at detecting T-2 and neosolaniol simultaneously in apples infected with T. roseum.

Damage to Trichothecium roseum caused by sodium silicate is independent from pH.

Trichothecium roseum is one of the most important postharvest pathogens in arid and semiarid regions. Sodium silicate (NaSi) and environmental pH have significant inhibitory effects on fungal growth. However, no study has addressed the relationship of NaSi and pH in combination and the effects on T. roseum. In this work, we showed that spore germination, germ tube elongation, and mycelial growth of T. roseum were significantly inhibited by various NaSi concentrations, which had corresponding increasing pHs. Furthermore, these NaSi solutions showed a much greater impact than did pH treatments alone. The pathogenicity of NaSi-treated conidia on a model assay (conidia-inoculated apple fruit) was dramatically reduced, whereas no changes of pathogenicity were evident for the corresponding pH (various sodium hydroxide (NaOH) solutions) treatments. Fluorescent microscopy, using propidium iodide staining, showed damage of the plasma membranes of T. roseum conidia treated with both NaSi and NaOH, although the damage was more severe with NaSi. Leakage of proteins and sugars was significantly higher in NaSi-treated and NaOH-treated conidia than in untreated controls. In addition, serious damage was observed in the conidia exposed to NaSi for longer periods of time. Ultrastructural observations showed that treatment with either NaSi or NaOH caused a plasmolysis state and disorganized organelles. Taken together the results show that NaSi has inhibitory effects on T. roseum and that the inherent higher pH of NaSi solutions of higher concentrations simply acts as an enhancer of the inhibitory effects of NaSi.

BTH treatment caused physiological, biochemical and proteomic changes of muskmelon (Cucumis melo L.) fruit during ripening

UNLABELLED Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) is a chemical plant elicitor capable of inducing disease resistance in many crops. In this study, the climacteric fruit muskmelon (cv. Yujinxiang) was treated with BTH at 0.1g/L for assaying the changes in physiology, biochemistry and protein profile during ripening. The results showed that BTH treatment enhanced respiration rate, while reduced titratable acid content and retarded the decline of fruit firmness and ascorbic acid content. Ethylene production increased after BTH treatment at early stages of ripening, but decreased after 6days of treatment. Of the detected protein spots separated by means of 2-DE, 69 spots changed in abundance significantly after BTH treatment. Fifty-two spots out of 69 were identified using MALDI-TOF/TOF by blasting against NCBInr database. Functional classification revealed that the protein species identified were related to defense and stress responses, protein synthesis, destination and storage, energy metabolism, primary metabolism, cell structure, secondary metabolism, signal transduction and transporters. This study demonstrates an overview of major physiological, biochemical and proteomic changes in muskmelon fruit during ripening after BTH treatment and provides potentially useful information for maintaining fruit quality and delaying the ripening and senescence process. BIOLOGICAL SIGNIFICANCE The study offers new proteomic evidences for elucidating the regulatory mechanism of muskmelon fruit ripening by BTH treatment at proteomic level, and provides a valuable reference for further research on the relationship between fruit quality and induction disease resistance in BTH-treated fruits.

Chemical composition of cuticular waxes during fruit development of Pingguoli pear and their potential role on early events of Alternaria alternata infection

To elucidate the role of fruit wax in fungal infection, changes in chemical composition of wax during fruit development of Pingguoli pear, and their role in Alternaria alternata infection were studied. Results showed that wax content increased during fruit development. Fruit harvested 130 days after full bloom (DAFB) had a peak wax content that was eight times higher than from fruit at 100 DAFB. There were differences in the relative chain-length distribution of wax classes during development. Alkanes were major components during early development, whereas alkanes and triterpenoids predominated during late development. Results of in vitro tests showed that conidial germination and mycelial growth of A. alternata could be inhibited by wax extracted from the fruit surface at different developmental stages. These results shed new light on the chemical basis for wax involvement in fungal infection.

The Role of Reactive Oxygen Species in ASM-Induced Disease Resistance in Apple Fruit

Blue mould caused by Penicillium expansum is one of the most important postharvest diseases of apple fruit. The present study was to evaluate how disease resistance in apple fruit (cv. Fuji) was affected by the dipping of acibenzolar-S-methyl (ASM) and diphenylene iodonium (DPI), a NADPH oxidase specific inhibitor. Lesion diameter on the fruit inoculated with P. expansum was significantly (P ≤ 0.05) decreased by dipping with 0.1 g/L ASM. Decreased lesion development was associated with the accumulation of hydrogen peroxide (H2O2), release of superoxide anion (O2 −), enhancement activities of NADPH oxidase (NOX), superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR). Antioxidants content including ascorbic acid (AsA) and reduce glutathione (GSH) was also induced by ASM treatment. While catalase (CAT) activity was inhibited by ASM dipping. Compared with ASM treated fruit, fruit treated with DPI prior to ASM treatment exhibited bigger lesion diameter. Moreover, DPI treatment inhibited ASM-induced H2O2 and O2 − accumulation, the increase of the activities of NOX, SOD, APX, GR and content of AsA and GSH. These results suggest that pretreatment with DPI prevented accumulation of ROS induced by ASM and showed serious disease symptoms, which showed the important role of ROS in ASM-induced resistance in apple fruit.

Effects of nitric oxide on growth of Fusarium sulphureum and its virulence to potato tubers

The antifungal activity of nitric oxide (NO) on Fusarium sulphureum in vitro and curative or preventive efficacy against dry rot in potato tubers was studied. We report that NO released by sodium nitroprusside (SNP) aqueous solution strongly inhibited spore germination and mycelial growth of F. sulphureum in a concentration-dependent manner. When treated with SNP, the fungus, under scanning electron microscopy, appeared distorted with irregular hyphal growth. Transmission electron microscopy observations documented further ultrastructural alterations of hyphae treated with SNP, and these changes included abnormally contracted, distorted hyphal cell walls, large empty cavities in the cytoplasm and even malformed hyphae. Furthermore, SNP was effective at curing and preventing dry rot in potato tubers in vivo. These findings highlight NO as a promising natural fungicide that could partially substitute for the utilization of synthetic fungicides in potato tubers.