ULTRASTRUCTURE OF CONIDIOGENESIS AND CONIDIA IN 2 SPECIES OF SEPTORIASENSU-LATO

Conidiogenesis and conidial morphology of Septoria quercicola and S. a ceris was studied with light (LM) and transmission electron microscopy (TEM) in vivo and in vitro on three media. No fundamental differences in conidiogenesis were observed between these species. Ontogeny of co nidia is holoblastic, and after delimitation by a transverse septum, c onidia are liberated schizolytically. Proliferation of the conidiogeno us cell can be percurrent or sympodial, and three categories of conidi ogenous cells occur: (i) annellides, (ii) sympodulae, and (iii) cells proliferating both percurrently and sympodially. Conidiogenous cells o f the last category were only observed in vivo, and most had a number of percurrent and one or two terminal sympodial proliferations. Annell ides with close annellations had been interpreted as phialides with pe riclinal thickenings in LM. After secession, a majority of conidia of S. quercicola and S. aceris developed noncellular, mucoid appendages o n either end, visible in LM and TEM; in S. quercicola appendages were formed in vivo and in vitro, in S. aceris only in vitro. No influence of either illumination (diffuse daylight or near-UV) or medium (OA, CM A, 2% MEA) was observed on qualitative aspects of conidiogenesis. The data are compared with those of S. chrysanthemella and their significa nce to Septoria systematics is discussed. The relation with Septoriell a in respect of ontogeny of mucoid appendages is assessed.