I. Spore Attachment and Invasion.- 1. Adhesion of Fungi to the Plant Surface: Prerequisite for Pathogenesis.- 2. Signaling for Infection Structure Formation in Fungi.- 3. The Plant Cell Wall as a Barrier to Fungal Invasion.- 4. Rust Basidiospore Germlings and Disease Initiation.- 5. Attachment of Mycopathogens to Cuticle: The Initial Event of Mycoses in Arthropod Hosts.- 6. The Fate of Fungal Spores in the Insect Gut.- 7. Candida Blastospore Adhesion, Association, and Invasion of the Gastrointestinal Tract of Vertebrates.- 8. Infectious Propagules of Dermatophytes.- II. Fungal Spore Products and Pathogenesis.- 9. Melanin Biosynthesis: Prerequisite for Successful Invasion of the Plant Host by Appressoria of Colletotrichum and Pyricularia.- 10. The Plant Cuticle: A Barrier to Be Overcome by Fungal Plant Pathogens.- 11. Appearance of Pathogen-Related Proteins in Plant Hosts: Relationships between Compatible and Incompatible Interactions.- 12. The Role of Cuticle-Degrading Enzymes in Fungal Pathogenesis in Insects.- 13. Potential for Penetration of Passive Barriers to Fungal Invasion in Humans.- 14. Dihydroxynaphthalene (DHN) Melanin and Its Relationship with Virulence in the Early Stages of Phaeohyphomycosis.- III. Host Response to Early Fungal Invasion.- 15. Invasion of Plants by Powdery Mildew Fungi, and Cellular Mechanisms of Resistance.- 16. Induced Systemic Resistance in Plants.- 17. The Plant Membrane and Its Response to Disease.- 18. The Fungal Spore: Reservoir of Allergens.- 19. Conidia of Coccidioides immitis: Their Significance in Disease Initiation.- 20. Cell-Mediated Host Response to Fungal Aggression.- 21. Suppression of Phagocytic Cell Responses by Conidia and Conidial Products of Aspergillus fumigatus.- IV. Molecular Aspects of Disease Initiation.- 22. Molecular Approaches to the Analysis of Pathogenicity Genes from Fungi Causing Plant Disease.- 23. Current Status of the Molecular Basis of Candida Pathogenicity.- Taxonomic Index.

The Fungal spore and disease initiation in plants and animals

Light and electron microscopy were used to describe the mode of penetration by the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin into corn, Zea mays L. After inoculation with a foliar spray of conidia, germinating hyphae grew randomly across the leaf surface. Often a germ tube formed from a conidium and elongated only a short distance before terminating its growth. Not all developing hyphae on the leaf surface penetrated the cuticle. However, when penetration did occur, the penetration site(s) was randomly located, indicating that B. bassiana does not require specific topographic signals at an appropriate entry site as do some phytopathogenic fungi. Long hyphal structures were observed to follow the leaf apoplast in any direction from the point of penetration. A few hyphae were observed within xylem elements. Because vascular bundles are interconnected throughout the corn plant, this may explain how B. bassiana travels within the plant and ultimately provides overall insecticidal protection. Virulency bioassays demonstrate that B. bassiana does not lose virulence toward the European corn borer, Ostrinia nubilalis (Hubner), once it colonizes corn. This endophytic relationship between an entomopathogenic fungus and a plant suggests possibilities for biological control, including the use of indigenous fungal inocula as insecticides.

Colonization of corn, Zea mays, by the entomopathogenic fungus Beauveria bassiana.

Liquefaction of Autographa californica nucleopolyhedrovirus-infected insects is dependent on the integrity of virus-encoded chitinase and cathepsin genes

Cuticle-degrading enzymes of entomopathogenic fungi: Synthesis in culture on cuticle

Pathogenic fungi are important natural regulators of insect populations. However, many attempts to harness their potential for pest control have met with comparatively minor commercial success. Studies on mechanisms of pathogenesis have yet to contribute to the development of more efficient mycoinsecticides, but new insights into the pathogenic process are laying the groundwork. Significant progress has been made in particular in understanding enzymes involved with the penetration of host cuticle and the role of insecticidal toxins. Insect cuticle comprises up to 70% protein and it is not surprising that extracellular fungal proteases appear to be particularly important in the penetration process. Subtilisins, chymotrypsins, trypsins and metalloproteases, usually with multiple isoforms of each, provide an impressive backed-up arsenal. Pathogenic fungi produce a wide variety of toxic metabolites, which vary from low molecular weight products of secondary metabolism to complex cyclic peptides and proteolytic enzymes. Comparatively few compounds have been found in diseased insects, in quantities sufficient to account for symptoms of mycosis. An exception, a family of cyclic peptides called the destruxins, are dealt with in detail. The potential for synergy between toxins is explored also.

J. Leopold

Papers

Action of enzymatic systems of Beauveria bassiana on the cuticle of the greater wax moth larvae (Galleria mellonella)