Phylum Zygomycota

Most species in the phylum Zygomycota (ZIE-goh-mie-KOH-tuh) are terrestrial organisms found primarily in soil that is rich in organic matter. The hyphae of zygomycetes are coenocytic. Rhizopus stolonifer, the common bread fungus shown in Figure 26-4, is a zygomycete. The hyphae that anchor the mold to the surface of the bread and that penetrate the bread's surface are called rhizoids (RIE-ZOYDZ). Digestive enzymes produced by rhizoids break down the bread to release nutrients. Other hyphae, called stolons (STOH-lahnz), grow across the surface of the bread.

Sexual reproduction in zygomycetes is called conjugation. Conjugation in fungi occurs when the hyphae of two compatible mating types (parents) meet. Short branches form on the hyphae of both types and grow outward until they touch each other. A septum forms near the tip of each branch, and a cell called a gametangium develops. A gametangium (GAM-uh-TAN-jee-uhm) is a sexual reproductive structure that contains a nucleus of a mating type. The nucleus within each parent's gametangium divides several times. When the gametangia fuse, the nuclei mix and form into pairs, each pair containing a nucleus from each mating type.

figure 26-4

During sexual reproduction zygomycetes produce gametangia.The nuclei from both mating types fuse and eventually produce genetically diverse spores.

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