Meiosis, septal pore architecture, and systematic position of the heterobasidiomycetous fern parasite Herpobasidium filicinum

Abstract

Meiosis, spindle pole body cycle and septal pores in Herpobasidium filicinum were examined using light and electron microscopy and compared with findings in the Uredinales and other simple-pored heterobasidiomycetes. The septal pore apparatus in Herpobasidium filicinum is rustlike, and the nuclear characteristics are also similar but not identical to those found in the Uredinales. Some details, such as the spindle pole body behaviour at prophase, the presence of a complete wrapping of endoplasmic reticulum surrounding the nucleus during division, the extension of the spindle pole body into the cytoplasm during division, and the nucleolus behaviour, distinguish Herpobasidium filicinum from the rusts. On the other hand, nuclear division and spindle pole body characteristics in Herpobasidium filicinum show some features common with Cryptomycocolax abnorme. However, Herpobasidium filicinum shares more important nuclear features with Pachnocybe ferruginea, Eocronartium muscicola, Helicobasidium mompa, and Helicobasidium brebissonii than with the Uredinales or Cryptomycocolacales. Apart from the phylogenetic implications of the ultrastructural data, the most interesting observation in the present work is the unusual type of meiosis. No evidence for meiosis II was found in basidia of Herpobasidium filicinum. Instead, the genesis of the interphase I spindle pole body in Herpobasidium filicinum is essentially identical to the basidiomycetous postmeiotic and intermitotic spindle pole body duplication. Key words: Herpobasidium filicinum, heterobasidiomycetes, meiosis, septal pore, spindle pole body, ultrastructure.