Introduction to Fungi, Third Edition

PLEOSPORALES
465
Fig17.5 Ascochyta pisi. (a) Pycnidium seen from above, showing a cirrhus of conidia oozing from the ostiole. (b) Conidia
(pycnidiospores). (c) Portion of pycnidium wall in section, showing origin of pycnidiospores.
Fig17.6 Phoma medicaginis. (a) View of the ostiole of a pycnidium from above, showing the angular appearance of the wall surface
comprising a textura angularis. (b) Conidia (pycnidiospores), most of them containing two lipid droplets. (c) Pigmented chlamydospores
formed by old hyphae embedded in agar.The light-refractive globose bodies inside the chlamydospores are lipid droplets.
b-conidia distinguishes Phoma from Phomopsis,
which belongs to an altogether different group
(see p. 373). The pycnidiospores often ooze out
from the ostiole as a tendril (cirrhus).
The conidiogenous cells of Phoma are very
small, and details of conidium development are
difficult to discern with the light microscope
(Fig. 17.7b). Brewer and Boerema (1965) have
therefore studied spore development with the
electron microscope. They described the process
of spore formation as a monopolar, repetitive
budding of the small, undifferentiated cells of
the pycnidial wall. As repeated spore formation
occurs, the apex of the conidiogenous cell