Ultrastructural studies of the effects of tetraconazole on the barley-powdery mildew host pathogen complex

The effects of tetraconazole (TC), a systemic triazole fungicide, were investigated on the fungal haustoria and the plant leaf cells. TC caused thickening of the haustorial wall, modifications of the extrahaustorial membrane and matrix, and deposition of polysaccharidic plant materials around the haustoria leading to their encapsulation. Appositions of similar polysaccharides were frequently observed also in the walls of non-penetrated surrounding epidermal cells and sometimes of some underlying mesophyll cells. No changes were found in uninoculated TC-treated leaves, and haustorial encapsulation occurred very rarely in untreated leaves when the haustoria were damaged by removing the hyphae from the leaf surface. In mechanically wounded, uninfected healthy leaves, TC treatment did not increase polysaccharide deposition around the wounds.