Infection mechanisms of grapevine powdery mildew (Oidium tuckeri):<p>Comparative studies of the penetration process on artificial membranes and leaf epidermis

Abstract

In order to study host-pathogen interfaces and relationships between grapevine and powdery mildew, an infection mode! was established. The model consists of synthetic membranes(≥ 0.4 μm) floating on liquid substrates; the membrane representing the cuticle of the host plant. The preparation of membranes and methods to test their impermeability and elasticity are described. The best results are obtained with membranes consisting of methacrylate polymers.
On membranes layered on various substrates germinating conidia and germtubes were observed with light and scanning electron microscope and compared to the natural infection process on leaf surfaces. On membranes germination and initial growth seem to be controlled by air humidity which depends on the osmotic value of the liquid substrate. As shown the infection pegs of Oidium tuckeri are able to perforate synthetic membranes which should be resistant to enzymes. This implies that under our experimental conditions penetration is a mechanical process. Participation of enzymes under natural conditions can, however, not be excluded.