What Is the Life Cycle of Rhizopus?

Rhizopus, or bread mold, has branching life cycles depending on whether it was produced sexually or asexually. Zygospores are fungal seeds that are made from sexual reproduction, a notable feature of bread mold’s group, the Zygomycota. The other kind of spores is called sporangiospores.

The sporangiospores are produced from fibers or hyphae that stand upright from the food the bread mold lands on. They possess black bulbous tips that contain the tiny spores. When conditions are right, the tips break open and the spores are released to be dispersed by wind. These spores are haploid, containing half the number of chromosomes of their zygospore cousins.

Zygospores are made when two adjacent hyphae of genetically differing bread mold strains meet. Rather than sexes, the two distinct kinds of mates are called plus and minus in fungi. When a plus strain of bread mold meets a minus strain, the two hyphae create structures, called gametangia. They fuse and exchange chromosomes in a process called karyogamy. Zygospores are held in place by suspensor cells made up of the former gametangia. They have thick coats to prevent drying out or destruction from ultraviolet rays.

Karyogamy only occurs when conditions are unfavorable for the other kind of growth. Otherwise, bread mold generally propagates via asexual reproduction. When the zygospore germinates, it creates more haploid sporangiospores via meiosis and new bread mold is produced.