Adhesion to the host surface is the first step for successful plant pathogen development and has been reported to be associated with both passive and active processes. For conidia of Venturia inaequalis, which depend on leaf wetness for germination, this process has not yet been described. Conidia of V. inaequalis adhered to wet hydrophobic surfaces immediately after contact to the surface, hours before initiation of germination. Attachment of nongerminated conidia was much better on hydrophobic surfaces, such as apple leaves and polystyrene, than on hydrophilic glass. Conidia released adhesive material localized in a droplet named spore tip glue (STG) at the spore apex which interacted with a contact surface only when water was present. Histochemical investigations indicated the presence of proteins and carbohydrates in STG, lectin labeling the presence of beta-galactose and N-acetylglucosaminyl residues. Transmission electron microscopy revealed two phases in the STG at the tip of dry mature conidia; as STG was present on the outer side of the intact fungal cell wall its formation should be associated with the secretion of glue through pores of the conidial wall. Surface-active substances affected the adhesion of conidia to hydrophobic surfaces stressing the importance of hydrophobic interactions. The use of protein biosynthesis inhibitors did not affect adhesion of conidia indicating that the adhesive material was preformed. It is concluded that the coincidence of STG, contact to a hydrophobic surface, and free water are essential for the adhesion of V. inaequalis conidia.

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Infection structures of Microdochium bolleyi on barley roots and coleoptiles Microdochium bolleyi grows within roots and coleoptiles of barley either leading to a damage of the tissue or to a symptomless infection. The present work investigated whether these different types of infection are correlated with different infection structures of the fungus. Two types of hyphae were formed infectmg either the rhizodermis or the epidermis. The fungus spread within the cortex only, not affecting the endodermal cells or the vascular tissue. The extend to which the roots were damaged depended on the infection density. Differences in the structure of hyphae formed in symptomless or necrotic parts of the roots were not observed. In both, roots and coleoptiles, hyphae were detected in dead cells only.

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