Antifungal Activity and Action Mechanisms of 2,4-Di-tert-butylphenol against Ustilaginoidea virens.

Ustilaginoidea virens is a destructive phytopathogenic fungus that causes false smut disease in rice. In this study, the natural product 2,4-di-tert-butylphenol (2,4-DTBP) was found to be an environmentally friendly and effective agent for the first time, which exhibited strong antifungal activity against U. virens, with an EC50 value of 0.087 mmol/L. The scanning electron microscopy, fluorescence staining, and biochemical assays indicated that 2,4-DTBP could destroy the cell wall, cell membrane, and cellular redox homeostasis of U. virens, ultimately resulting in fungal cell death. Through the transcriptomic analysis, a total of 353 genes were significantly upregulated and 367 genes were significantly downregulated, focusing on the spindle microtubule assembly, cell wall and membrane, redox homeostasis, mycotoxin biosynthesis, and intracellular metabolism. These results enhanced the understanding of the antifungal activity and action mechanisms of 2,4-DTBP against U. virens, supporting it to be a potential antifungal agent for the control of false smut disease.

Natural occurrence of ustiloxins in rice from five provinces in China and the removal efficiencies of different milling steps.

BACKGROUND: The widespread incidence of "false smut" disease in rice has caused extensive ustiloxin contamination around the world. Until now there has been a lack of knowledge regarding the natural occurrence of ustiloxins in paddy. The development of efficient removal methods is also still a challenge that remains unexplored. RESULTS: In the current study, three main ustiloxins - ustiloxin A (UA), ustiloxin B (UB), and ustiloxin G (UG) - were determined simultaneously by ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in 206 paddy samples collected in 2021 from five rice-producing provinces in China. The predominant ustiloxin was UA with an occurrence of 46.1% and an average concentration of 49.71 µg kg-1 . This was followed by UB (31.1%, 13.31 µg kg-1 ) and UG (18.4%, 9.19 µg kg-1 ). No targeted ustiloxins were detected in white rice samples randomly collected from supermarkets in Shanghai. To reveal the causes, two approaches were tested for the removal of the ustiloxins: most of the targeted ustiloxins (>93%) were removed in brown rice by husking and, subsequently, all targeted ustiloxins (100%) were removed by whitening. CONCLUSION: A wide distribution of ustiloxins was discovered in paddy samples in this study. The UA contaminations were significantly different depending on their origin, with the highest occurrence in paddy from Shanghai and Jiangsu, southeast coast provinces in China. Contamination by UG was also found in paddy for the first time and was strongly correlated with those of UA and UB. A combination of husking and whitening has been verified to be a practicable and promising way to ensure efficient removal and food safety. © 2023 Society of Chemical Industry.