Immunocytochemical studies of the infection mechanisms of <em>Botrytis fabae</em> I. The fungal extracellular matrix in penetration and post-penetration processes.

Extracellular matrices associated with conidia and germ tubes of Botrytis fabae (Sard.) sporelings grown on Vicia faba L. leaves were clearly visualized by epi-fluorescence microscopy following immunolabelling with the monoclonal antibodies, BC-KH4 and BC-FD7-G9. These antibodies were raised against surface washings of B. cinerea, are directed against B. cinerea and B. fabae, and are known to recognize carbohydrate epitopes on a glycoprotein. Both BC-KH4 and BC-FD7-G9 also labelled matrix material located at the surface of penetration and infection hyphae inside the leaf tissue by epi-fluorescence microscopy. Such matrix material was not visible by DIC microscopy. Immunoelectron microscopy of B. fabae-infected leaf tissue, prepared by progressive low-temperature dehydration and embedding in acrylic resin, allowed further investigation of the spatial distribution of the antibody-binding sites. An abundance of BC-KH4 and BC-FD7-G9 antigenic sites were observed throughout the fibrillar-like matrix material surrounding the germ tubes on the leaf surface and the infection hyphae inside the host cells. However, close examination of the V. faba B. fahae interface inside the host tissue showed that this fibrillar material extended some distance from the surface of the infection hyphae and through the swollen epidermal and mesophyll cell walls. Such fibrillarmatrix material is though to be of fungalorigin. the possible role(s)of this matrix material in the infection process are discussed. Double-immunolabelling studies using the BC-KH4 MAb and a polyclonal antiserum directed against oligosdaccharides containing (1-3)-glocose were carried out in order to localize and distinugish between the examination of the interactions of the fungalmatrix components with the host walls and degenerate host cytoplasm. Finally, inward curling of the leaf cuticle suggested that mechanical pressure is involved in the penetration process. [ABSTRACT FROM AUTHOR]