Introduction to Fungi, Third Edition

380 HYMENOASCOMYCETES: PYRENOMYCETES
Fig12.45 Microscopy of Magnaporthe grisea. (a) Hydrated conidium of M. grisea showing the drop of mucilage exuded at the apex.
(b) Ungerminated conidium with dense cytoplasmic contents and developing vacuoles. (c) Conidium on a hydrophobic surface about
18 h after germination. Most cytoplasmic contents have been translocated into the appressorium which is laying down a dark
melanized wall. (d) SEM of a mature appressorium of M. grisea.Whereas the conidial cells have collapsed due to the loss of turgor
pressure, the appressorium is still turgid. (e) TEM of an appressorium penetrating a cellophane membrane.The appressorial wall is
heavily melanized with the exception of the basal region through which the penetration peg has emerged. A large vacuole (Vac) and
nucleus (Nuc) are visible inside the appressorium. (f,g) Formation of bulbous hyphae from an appressorium, some 36 h after
penetration of an onion epidermis. A thinner secondary hypha has already been produced (arrow). Micrographs in (d) and (e) kindly
provided by R. J. Howard; (d) reprinted fromValent (1997) with kind permission of Springer Science and Business Media;
(e) reprinted from Bourett and Howard (1990), by copyright permission of the National Research Council of Canada.Original
micrographs in f and g kindly supplied by A. J.Foster. (a c) to same scale; (f,g) to same scale.