Fusarium wilt of banana (Musa spp.) caused by Fusarium oxysporum f. sp. cubense (Foc) is one of the most serious banana fungal diseases in the world. Understanding the infection process of Foc is important for development of effective ways in disease control. In order to follow infection and colonization of this pathogen from root to rhizome and pseudostem tissues of banana, a highly pathogenic strain FJAT-3076 of Foc race 4 (Foc4) was transformed with gene encoding green fluorescent protein (GFP) and the fungus carrying gfp (FJAT-3076-GFP) was used to inoculate banana plants (Cavendish cv. B.F.). After inoculation for 3 to 10 d, it was observed that the conidia and their germ-tubes had penetrated into epidermis of young roots. The hyphae were found inside the root xylem 10 d after inoculation in the rhizome and pseudostem xylem after inoculation for 17 d. All plants infected by Foc died in 24 d after inoculation. It was also observed that Foc had spread all over the xylem and part of hyphae reached the pseudostem surface. Hyphal population was found the highest in the pseudostem, lower in root and least in rhizome. Field survey confirmed that Foc4 were mostly present in the base of pseudostem and less in the rhizome. Thus, effective prevention of the Foc hyphae movement from the rhizome up to the pseudostem might delay or control banana wilt disease.

Zuota is regarded as the king of Tibetan medicine. However, the major starting material of Zuota is mercury, which is one very toxic heavy metal. This has aroused serious doubts on the biosafety of Zuota containing drugs. In this study, we quantified the Hg contents in four Zuota samples, monitored the release of Hg in simulated gastric/intestinal juice and evaluated their cytotoxicity to Caco-2 cells. Our results showed that the Hg contents in Zuota samples were in the range of 566-676 mg/g. Fortunately, the release of Hg from Zuota samples was very low in simulated gastric juice, and much lower in simulated intestinal juice. Direct contact of Zuota with Caco-2 cells led to dose-dependent cytotoxicity, including activity loss and membrane leakage. The toxicity was closely related to apoptosis, because the caspase 3/7 levels of Caco-2 cells increased after the exposure to Zuota. Interestingly, Zuota samples inhibited the oxidative stress at low concentrations, but the toxicity could be relived by antioxidants. The possible toxicity should be attributed to the cellular uptake of Zuota particulates. Beyond the cytotoxicity, significant differences among Zuota samples from different institutions were observed, suggesting that the preparation process of Zuota had meaningful influence of its biosafety. The implications to the safety and clinical applications of Zuota are discussed.

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