Studies of conidial anatomy and conidiogenesis in Sporoschisma nigroseptatum using light and electron microscopy

The results of an ultrastructural study of the conidial anatomy and conidio genesis in Sporoschisma nigroseptatum are presented. The development of the conidial chain involves endogenous conidial ontogeny, apical wall-building , and retrogressive conidial delimitation followed by cessation of apical w all-building, then replacement ring wall-building of additional retrogressi vely delimited conidia, and extrusion of the true conidial chain through th e terminal aperture of the conidiogenous cell. Maturation of conidia involv es deposition of two inner wall layers and formation of five distosepta. Co nidial chains secede schizolytically. No proliferation of the conidiogenous cell occurs and the conidium is delimited by a cross wall that is disconti nuous with the periclinal wall. Each conidium has polar plug-and-socket-lik e structures that are interlocked between adjacent conidia along the conidi al chain. Similar plug-and-socket-like structures are also seen in other Sp oroschisma species. The taxonomy of Chalara is also briefly discussed with reference to patterns of conidial wall-building.