Reproduction

           Morchella esculenta is a fungus that follows a dikaryotic life cycle. In this life cycle, the only diploid phase is the very short sporophyte stage. The sporophyte of the morel is a very complex ascomycete structure. It is spongelike with many openings called apothecia that are raised above the ground to enable the dispersal of ascospores (Volk 1990). The ascospores will be released through the operculum and can be shot up to several meters away from the sporophyte for the life cycle to repeat itself. The ascospores that are released can be found within an ascus. An ascus is a sac-like structure that has been found to contain eight ascospores, which are the beginning of the life cycle of M. esculenta (Volk 1990).

         The life cycle starts out as a haploid ascospore produced from the sporophyte. After the ascospores are released, they have been found to germinate almost immediately (Volk 1990). After germination of the ascospores, multinucleate hyphae begin to grow. From the multinucleate hyphae growth there are two different ways that the life cycle of M. esculenta can go, the deciding factor on which way the life cycle will take is dependent upon when plasmogamy takes place (Volk 1990).

         The first pathway will proceed to grow without undergoing plasmogamy. The primary mycelia will round up and grow thicker cell walls to preserve the nuclei. This type of growth will form sclerotia, which is a structure with very thick cell walls that enable the fungus to survive through harsh conditions (Leonard 1992). The sclerotia may preserve itself throughout winter and form fruiting hyphae in the spring (Volk 1990). This path is mainly taken when conditions around the fungus do not favor any further vegetative growth. This could mean anything from a lack of nutrients, to unfavorable growing temperatures or water levels.  The fungus has also been found to follow this path when certain nutrients are present, one of which is sheep manure  (Volk 1990). 

           The fungus will go through the second pathway when conditions are optimal for further growth and there is an interaction between two compatible primary mycelia (Volk 1990). Once the two primary mycelia have undergone  plasmogamy and fused to create a secondary mycelium, another sclerotium is formed. The sclerotium then has two different paths that the cycle can take: myceliogentic germination or carpogenic germination. In myceliogenic germination the sclerotium forms back into a secondary mycelium and waits for optimal growing conditions to continue with its life cycle. When the sclerotium undergoes carpogenic germination, the fruiting body is then developed which quickly forms asci that contain ascospores and the cycle repeats itself (Volk 1990).

            There is no set time for each stage of the life cycle. M. esculenta can take a very long time to form into a fruiting body and produce ascospores for reproduction. The cycling between the mycelia stages and sclerotia stages can last for hundreds of years. Because of the unusual life cycle of the morel and the unpredictability of each stage of the cycle, little is known about what causes carpogenic germination and what causes mycilogenic germination. This frustrates not only researchers trying to figure more out about M. esculenta, but also the farmers who are trying to artificially cultivate the mushrooms to make a profit (Leonard 1992).

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