The Life-History ofChristiansenia Pallida, A Dimorphic, Mycoparasitic Heterobasidiomycete

Christiansenia pallida Hauerslev, a heterobasidiomycetous parasite of Phanerochaete cremea (Corticiaceae), was cultivated and studied with light and electron microscopes. Monokaryotic basidiospores bud as yeasts. Compatible cells conjugate and dikaryotic mycelia develop when yeast cells are grown together with the host on artificial media. Thread-like, monokaryotic hyphal outgrowths originate from clamps and function as haustoria, penetrating host cells. In its parasitic stage, Christiansenia pallida propagates chiefly by conidia. These are formed on short, terminal, monokaryotic, conidiogenous cells; conidia originate side by side, then fuse to form one dikaryotic zygoconidium. Dikaryotic conidia germinate to produce short-celled, dikaryotic hyphae which bear haustorial branches. Dikaryotic conidia are capable of dedikaryotization, thereby producing monokaryotic yeast cells. Usually, in a later stage of ontogeny, basidia develop on dikaryotic hyphae. Basidial morphology is rather variable, but suburniform basidia are typical. More than four sterigmata often are formed.