Experimental studies on the morel.

摘要

Although there is substantial general interest in the morel (Morchella species) because of the delicious flavor of its "mushrooms" and because of the air of mystery about this fungus due to its rarity in nature and its reticence in being cultured, comparatively little is known about its biology and life cycle. This study represents the first detailed compilation of the morel life cycle based on previous literature and recent cultural, cytological, and genetic studies in this laboratory.;The first study in this thesis contains the first published photographs of many of the aspects of the morel life cycle including the cytological details of vegetative mycelium growth, fruiting body initiation, ascus ontogeny, heterokaryon formation, and sclerotium development.;The second study focused on the environmental and physiological factors influencing sclerotium formation. A number of nutrients were tested in agar culture and in the jar method of sclerotium production; various additives were tested with rye.;The last and potentially most significant of the studies presents three independent lines of evidence to demonstrate heterokaryon formation between monoascosporous strains of the morel: (1) Cultural studies demonstrated that the putative heterokaryon was unlike either of the "parental" strains in its morphology. (2) Cytological studies following hyphal fusion between two monoascosporous isolates showed that many of the cells of this putative heterokaryon contained nuclei in pairs, a condition which was not found in monoascosporous isolates. This dikaryotic-like pairing was also observed in some fruiting body cells as well, suggesting a link between the vegetative heterokaryon and the fruiting body. (3) Genetic complementation of two drug resistance markers demonstrated that two monoascosporous strains do form a heterokaryon. Some of the cells of this putative heterokaryon also exhibit nuclear pairs. These three lines of evidence demonstrate for the first time that there is a heterokaryotic phase in the life cycle of the morel.