Adhesion of Cochliobolus heterostrophus Conidia and Germlings to Leaves and Artificial Surfaces

Braun, E. J., and Howard, R. J. 1994. Adhesion of Cochliobolus heterostrophus conidia and germlings to leaves and artificial surfaces. Experimental Mycology 18, 211-220. We have examined the nonspecific attachment of Cochliobolus heterostrophus germlings to a variety of surfaces (glass, cellophane, Mylar, polystyrene, Teflon, maize leaves) in an effort to more fully characterize this important stage of pathogenesis. Washing experiments showed that conidia began adhering to glass just prior to germ tube emergence, about 20 min after hydration and inoculation. By 50-60 min after inoculation, over 90% of the germinating conidia resisted washing and remained firmly attached. Similar results were obtained with the other surfaces. Both sodium azide and cycloheximide prevented attachment, indicating that metabolic activity was required for adhesion. Light microscopy and cryo scanning electron microscopy were used to document a temporal and spatial relationship between attachment, appearance of extracellular matrix materials, and germ tube emergence. Attachment of conidia to the substratum was correlated with the appearance of extracellular material exuded from the tips of conidia just prior to germination. The two-layered sheath of matrix materials associated with germ tubes also surrounded appressoria and appeared to aid in attachment of these structures to leaves and artificial surfaces. We conclude that extracellular matrix is produced and/or secreted within 20 min of hydration and serves in the nonspecific attachment of germlings to the substrate.