Abstract
The effects of osthol, a plant coumarin, on morphology, sugar uptake and cell wall components of Fusarium graminearum were examined in vitro by electron microscopy,(14)C-labelling and enzyme activity detection. The results revealed that osthol could inhibit the hypha growth of F. graminearum by decreasing hyphal absorption to reducing sugar. After treatment with 100 microg.mL(-1) osthol for 24 h, many hyphal fragments of F. graminearum appeared. Microscopy observation showed that the cell walls of hyphal fragments blurred and the organelles of the cells degraded with the increasing vacuoles. The N-acetyl-D-glucosamine contents and chitinase activity both increased when hypha were treated with 100 microg.mL(-1) osthol, whereas the activity of beta-1,6-glucanase remained unchanged. When F. graminearum fed with (14)C glucose was treated with 100 microg.mL(-1)osthol, glucose contents decreased to the lowest level, while the contents in non-osthol treated controls remained unchanged. These results suggested that chitinase activity might be related to glucose starvation under osthol treatment, and that the appearance of hyphae fragments maybe the results of the promoted chitinase activity which itself triggered chitin degradation.
Highlights
Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe, is a major disease of wheat and has resulted in heavy yield losses in many areas of China, the largest wheat producer in the World [1, 2]
In vitro antifungal assays in our previous study had demonstrated that osthol could inhibit the growth of hyphae of F. graminearum with its EC50 value 56.94 μg·mL-1 [10]
With the increase of osthol concentration in potato dextrose agar (PDA) medium plates, the inhibitory effect against F. graminearum was enhanced through reducing the growth diameter on plates (Figure 1)
Summary
Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe (teleomorph: Gibberella zeae), is a major disease of wheat and has resulted in heavy yield losses in many areas of China, the largest wheat producer in the World [1, 2]. Plant disease control in China nowadays still relies mainly on the application of chemical agents. Our previous studies showed that osthol has a wide antifungal activity, with the EC50 values ranging from 21.15 μg·mL-1 to 61.62 μg·mL-1 against Botrytis cinerea, Colletotrichum mllsae, Fusarium graminearum, Phytophora capsici, Sclerotinia sclerotiorum and other phytopathogenic fungi [10]. As a natural plant toxin, osthol has been developed into biopesticides in our lab, its antifungal mechanism and mode of action against phytopathogens still remains unknown. We investigated the effects of osthol on F. graminearum, pathogen causing FHB, and a preliminary mechanism of action was studied and discussed
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