INTRODUCTION

Black bread mold is the common name for a species of fungus called Rhizopus stolonifer. Despite its name, this fungus also attacks substrates other than bread, including cheese and a variety of fruits and vegetables. Rhizopus grows by extending filaments, called hyphae, along the surface of a substrate and by penetrating the substrate with rootlike structures (also made up of hyphae) called rhizoids. Like all fungi, Rhizopus digests its food outside its body and then transports the digested nutrients inside.

Rhizopus is classified in the group Zygomycota, the zygospore fungi. The name for this group comes from the only diploid structure—called the zygosporangium—that exists in the entire life cycles of these organisms. In the accompanying animation we depict the life cycle of a zygospore fungus, which includes both sexual and asexual reproduction.

CONCLUSION

A close inspection of bread being attacked by black bread mold will reveal a cottony mass of filaments spotted with black dots. The cottony mass consists of thousands of hyphal strands, and the black speckles are the sporangia that are borne atop hyphal stalks. From their elevated positions, these sporangia can crack open and disseminate the spores to new substrates at distant locations.

If two fungi of opposite mating types meet, these organisms can reproduce sexually by fusing their nuclei. In this process, a tough zygosporangium forms. The zygosporangium can wait out the worst of environmental conditions for months, and then revive when environment conditions are again favorable. When they revive, the zygosporangia produce sporangia elevated on hyphal stalks. When the sporangia crack open, their spores disseminate, and, if the spores land on appropriate substrates, they will germinate and continue the life cycle of the fungus.

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Textbook Reference: Concept 22.3 Major groups of Fungi Differ in Their Life Cycles