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Fig. 5.2Examples of infection structures of plant-pathogenic fungi. (a) Diagrammatic representation of an appressorium
produced from a germinating spore. A narrow penetration peg develops from beneath the appressorium, to breach the
host cell wall, and then expands to produce an infection hypha. (b) An infection cushion composed of a tissue-like mass
of melanized hyphae,from which multiple penetration pegs invade the host plant. (c– e) Lobed hyphopodia of one of
the take-all fungi (Gaeumannomyces graminisvar. graminis) growing on a cereal stem base. (c) Shows the structures in
surface view, whereas (d) is a hyphopodium in side view. The arrowhead in (d) is a papilla (a localized ingrowth of the
wall of the plant cell that the fungus is attempting to penetrate) signifying that the plant cell is still alive and resisting
invasion. (e) Lobed hyphopodia of G. graminisproduced on the plastic base of a Petri dish. (f ) The hypothesized mode
of development of lobed hyphopodia by repeated stoppage, swelling and branching of a hyphal tip.