Bread Molds: (Zygomycota)

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A two-week old plate culture of Phycomyces is available for examination. This organism is a zygomycete fungus. DO NOT OPEN THE CULTURE!  Examine through the lid of your culture with the dissecting microscope.

Your culture will likely show asexual reproduction; notice the obvious, sporangia borne at the ends of upright branches of the coenocytic mycelium. These contain or produce a great many, small, spores which are easily wind distributed (DO NOT OPEN THE CULTURE)!  These spores may contaminate the building and cause allergic reactions in some persons). The upright sporangiophores may be connected to each other by stolons and to the medium by rhizoids. Most of these species are heterothallic, so two strains are required for successful sexual reproduction. This Potato Dextrose Agar (PDA) plate has the + and – mating types inoculated at opposite edges of the plate (note the markings on the bottom of the plate).

Examine the plate culture under the dissecting microscope. Check the edges where most of the mycelium is of one mating type. Then compare mid-way across the plate where the two mating types have converged. Where the two strains have grown together, you may be able to observe a line composed of structures called zygospores. In the zygomycetes, hyphae of the two strains contact each other and the hyphal tips each divide off to form a gamete cell. The two gamete cells, which are in contact, fuse to form the zygote. The zygote develops a thick, sometimes dark wall, and enters a resting period as a zygospore. Meiosis occurs inside this resting spore or inside a sporangium that grows out of it.

In the space below, illustrate what you have found of the life cycle of this zygomycete. If you cannot find both sexual and asexual reproductive structures, ask the instructor what to do about that. Be sure to connect the words to the appropriate structures with lines!

Life Cycle of Phycomyces (8 points)