This fungus is distributed throughout the world. One species is used to ferment rice into sake. Another species is used to inoculate soybeans to make tempeh. The genus is usually saprophytic but frequently attacks fruits and vegetables that have been injured. It occupies non-aquatic habitats and never produces motile spores. Sexual reproduction is by conjugation.

(A) Culture examination

(1) Examine a culture of Rhizopus. Note the appearance of the colony. What color are the hyphae? What are they? Can you see other structures that appear similar structures except for their white appearance? What are they?

(2) Examine the culture with a dissecting microscope. Is the mycelium branched? Are cross walls present? Note the characteristic formation of rhizoids, small root-like branches developed along the hyphae growing on the substrate.

(3) Focus on the dark colored structures. These are sporangia. The dark ones contain masses of mature sporangiospores. The whitish ones are not yet mature. The sporangial wall is very fragile and is frequently ruptured when preparing slides. The branch supporting the sporangium is called a sporangiophore.

(B) Wet mount

Prepare a wet mount of some of the mycelium with sporangia and examine with a compound microscope. Note the coenocytic mycelium. Locate a sporangiophore and sporangium. What color are the spores? Is the spore wall smooth or roughened?

(C) Sexual Reproduction

(1) To demonstrate sexual reproduction, 2 different strains of Rhizopus have been grown together. Examine a plate with a dissecting microscope. Find an early stage of conjugation in which short, lateral branches arise from separate hyphae and come into contact. The branches typically become enlarged and have a relatively dense mass of cytoplasm. They are the progametangia.

(2) Next find stages in which a cross wall has divided the progametangia into a terminal portion, the gametangium and a supporting cell called suspensor.

(3) The wall separating the plus (+) and minus (-) gametangia dissolves, the cytoplasm mixes, and nuclei pair. Nuclear fusion occurs and the cell formed by the former gametangia develops a thick, dark colored, rough wall. This is the zygospore. It can remain dormant, but eventually meiosis occurs. A sporangium arises from the zygospore, after which the haploid spores disperse.