Abstract:The effects of a triazol group fungicide tebuconazole on the infection process of Fusarium graminearum on wheat spikes were examined by means of electron microscopy and immuno-cytochemical labeling techniques. The results revealed that the conidia of the pathogen were able to germinate on the lemma, palea and ovary of the wheat spikes treated with fungicide 2 days before inoculation. However, the further extension of the hyphae was obviously inhibited. The germ tubers and hyphae became malformed. The penetration hyphae were never detected on these deformed hyphae on the host surface. The spikes treated 2 days after inoculation, the hyphae in the infected lemma, ovary and palea also exhibited a series of morphological and structural alterations. Treated the spikes 4 days after inoculation, hyphae were also obviously inhibited in the rachis. Immunocytochemical labeling with antiserum against deoxynivalenol (DON) revealed that Fusarium toxins was localized in the walls, cytoplasm, mitochondria and vacuoles of hyphae cell, and in the walls, cytoplasm members, chloroplast, cytoplasm and vacuoles of the host cells in the wheat spikes treated and untreated with the fungicide. However, the labeling density of the toxin in the fungicide-treated spikes was markedly lower than that of the untreated control.