Ultrastructure of conidium acid disjunctor development in the plant pathogenic fungus Monilinia vaccinii-corymbosi

Condium initials in Monilinia vaccinii-corymbosi developed acropetally in m oniliform chains. Each was multinucleate and covered by a two-layer wall co ntinuous with that of the initial below. An initial was delimited by the fo rmation of a basal septum. Developing conidia were spherical in shape and i nterconnected by constricted intercalary regions where septa were located. Disjunctors formed between the two lamellae comprising each septum. A disju nctor consisted of two conical structures with their broad bases facing one another and their tapering ends terminating in invaginations of wall mater ial continuous with the septal lamellae. Septal lamellae, wall invagination s and disjunctors labeled uniformly with WGA-ovomucoid-gold complexes indic ating the presence of chitin. Developing disjunctors displaced the septal l amellae causing them to produce conspicuous concave depressions in the cyto plasm at the ends of conidia. Conidium disarticulation occurred when the wa ll connecting adjacent conidia broke at the septum in each intercalary regi on. Disarticulated conidia tended to remain in long to short chains interco nnected by now elongated and spindle-shaped disjunctors. Mature conidia bec ame highly vacuolated and appeared to lack both lipid bodies and glycogen d eposits. Each was covered by a two-layered wall derived from the wall that originally covered conidium initials.