Spore Germination of and Carbohydrate Colonization by Morchella Esculenta at Different Soil Temperatures

Abstract

Few detailed data on the life cycle and ecology of morels have been reported from field studies. In this study, spore germination and saprophytic ability of Morchella esculenta in natural soil were investigated as related to progression of soil temperatures during the fruiting season. Ascospores germinated at temperatures as low as 2 C in vitro. However, spores buried in cellophane at morel sites swelled but did not produce germ tubes until the soil temperature exceeded approximately 10 C. Germination is inhibited as the soil continues to warm after fruiting body emergence (i.e., above 15 C). Spores did not remain viable after 1 yr near the soil surface. Sterile rye buried 2 wk in the field was readily colonized by M. esculenta when cased with site soil containing either spores or sclerotia when soil temperatures remained below 10 C. As temperature increased, only other saprophytes were isolated. Frequent observations of germling hyphal growth by a direct path to ungerminated spores suggests that heterocaryon formation could occur at this stage in the life cycle of M. esculenta. Despite the long-standing interest in morels by mycologists and mycophagists, little ecological information, beyond horticultural observation, has been reported from field studies. As stated by Callieux (1969), and recently reiterated by Delmas (1978), the methods for morel cultivation remain undefined and haphazard due to the lack of knowledge of their life cycle and ecology. Ower's (1982) report on ascocarp production from initially axenic culture on wheat berries may obviate the need to elucidate their life cycle in nature before they can be commercially cultivated. Nonetheless, the importance of fungi in nutrient cycling under cool soil conditions of spring would justify study of the ecology of this widespread ascomycete. This study explored M. esculenta Fr. (sensu Groves and Hoare) ascospore germination in vitro and in natural soil as related to temperature. Additionally,