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 cau sed thickening of the haustorial wall, modifications of the extrahaust orial membrane and matrix, and deposition of polysaccharidic plant mat erials around the haustoria leading to their encapsulation. Apposition s of similar polysaccharides were frequently observed also in the wall s of non-penetrated surrounding epidermal cells and sometimes of some underlying mesophyll cells. No changes were found in uninoculated TC-t reated leaves, and haustorial encapsulation occurred very rarely in un treated leaves when the haustoria were damaged by removing the hyphae from the leaf surface. In mechanically wounded, uninfected healthy lea ves, TC treatment did not increase polysaccharide deposition around th e wounds.