Orientation of the primary infectious structures of powdery mildew fungi (Blumeria graminis) and their adhesion to the surface of infected wheat (Triticum aestivum) leaves.

The anisotropic nature of the surface of highly elongated cereal leaves means that longitudinally and transversely oriented germinating conidia of phytopathogenic fungi could have different biological properties. We measured the angles between the long axis of the conidium, the axis of the plant leaf and the direction of the appressorial germ tube of the powdery mildew fungus Blumeria graminis f. sp. tritici on wheat leaves. Two main distribution patterns were observed. Normal appressorial germ tubes were associated with the longitudinal microrelief of the wheat leaves, whereas abnormal germ tubes tended to have a random distribution. The increased rotational mobility of these abnormal germ tubes may result from a reduction in their adhesion to the surface of plant cells. [ABSTRACT FROM AUTHOR]