Division (Phylum): : Zygomycota − Rakyat Biologi

Most of the Zygomycota live on decaying plant or animal matter in the soil but some are parasites on plants, insects or small soil animals. There are approximately 750 described species of Zygomycota. The term "Zygomycota" refers to the chief characteristic of the division; the production of sexual resting spores called “zygospores”. Most zygomycetes are saprophytic and their vegetative hyphae lack septa (i.e., they are aseptate).

One representative of this division, Rhizopus stolonifera, a common black bread mold

Rhizopus stolonifera (black bread mold)

This species is one of the most common members of this division. This organism causes the black bread mold that forms cottony masses on the surface of moist bread exposed to the air.

Asexual reproduction in Rhizopus occurs by spores (Figure 12). The mycelium of R. stolonifera is composed of three different types of haploid hyphae (another word for a filament). The bulk of the mycelium consists of rapidly growing submerged hyphae that are coenocytic (multinucleate) and aseptate (not divided by cross walls into cells or compartments). From the submerged hyphae, aerial hyphae called, stolons, are formed. The stolons form rhizoids wherever their tips come in contact with the substrate. Sporangia form on the tips of sporangiophores, which are erect branches formed directly above the rhizoids (Figure 10, 12). The sporangiophores support the asexual reproductive structures: the sporangia. Within a sporangium, haploid nuclei divide by mitosis and produce haploid spores. The cell wall that forms around each spore is black, giving the mold its characteristic color. The spores are released to the environment when the sporangium matures and breaks open. Each spore can germinate to produce a new mycelium.

Diagram illustrating the vegetative and asexual reproductive structures of Rhizopus sp.

Rhizopus sp. growing on peaches. (Asexual sporangiouphores)

Sexual reproduction in Rhizopus occurs only between different mating strains, which have been traditionally labeled as + and – types (or Strain 1 and Strain 2, as seen in Figure 12). Although the mating strains are morphologically indistinguishable, they are often shown in life cycle diagrams as different colors). When the two strains are in close proximity, hormones are produced that cause their hyphal tips to come together and develop into gametangia (Figure 11, 12), which become separated from the rest of the fungal body by the formation of septa. The walls between the two touching gametangia dissolve, and the two multinucleate protoplasts come together. The + and - nuclei fuse in pairs to form a young zygospore with several diploid nuclei. The zygospore then develops a thick, rough black coat and becomes dormant, often for several months. Meiosis occurs at the time of germination. The zygospore cracks open and produces a sporangium that is similar to the asexually produced sporangium, and the life cycle begins again.

Rhizopus stolonifera reproduces by sexual reproduction (gametangia, sporangia, & zygospores).