Ultrastructure of conidiogenesis and conidia in two species of Septoria sensu lato

Abstract

Conidiogenesis and conidial morphology of Septoria quercicola and S. aceris 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 conidia is holoblastic, and after delimitation by a transverse septum, conidia are liberated schizolytically. Proliferation of the conidiogenous cell can be percurrent or sympodial, and three categories of conidiogenous cells occur: (i) annellides, (ii) sympodulae, and (iii) cells proliferating both percurrently and sympodially. Conidiogenous cells of the last category were only observed in vivo, and most had a number of percurrent and one or two terminal sympodial proliferations. Annellides with close annellations had been interpreted as phialides with periclinal thickenings in LM. After secession, a majority of conidia of S. quercicola and S. aceris developed oncellular, mucoid appendages on 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 ither illumination (diffuse daylight or near-UV) or medium (OA, CMA, 2% MEA) was observed on qualitative aspects of conidiogenesis. The data are compared with those of S. chrysanthemella and their significance to Septoria systematics is discussed. The relation with Septoriella in respect of ontogeny of mucoid appendages is assessed.

Key Words:

• Conidial appendage
• phialide
• TEM
• Septoria quercicola
• Septoria aceris
• Phloeospora aceris