Surface characteristics of necrotrophic secondary hyphae produced by the bean anthracnose fungus, Colletotrichum lindemuthianum

During infection of bean (Phaseolus vulgaris), the hemibiotrophic anthracno se pathogen, Colletotrichum lindemuthianum, initially produces biotrophic p rimary hyphae that are large-diameter and entirely intracellular, followed by necrotrophic secondary hyphae that are narrower and either intercellular or intracellular. In the present study, transmission electron microscopy o f infected tissues prepared by high-pressure freezing and freeze-substituti on showed that secondary hyphae have much thinner cell walls (25-40 nm) tha n primary hyphae (100-130 nm) and are not surrounded by an extracellular ma trix. Immunofluorescence labelling with a panel of monoclonal antibodies sh owed that glycoproteins which are present on conidia, germ-tubes, appressor ia, primary hyphae and mycelium grown in vitro are absent from the surface of secondary hyphae. Chitin, detected with the lectin wheat germ agglutinin , was the only surface component shared by secondary hyphae and the other f ungal cell types. The results suggest that the fungal cell surface becomes modified during necrotrophic growth, with none of the glycoproteins associa ted with earlier stages of the infection process being produced.