• Saprophytic (able to live on decaying organic matter).
• Broad Hyphae
• 3-25 um in diameter; average 12 um.
• Infrequently septate, with nonparallel sides.
• Hyphae may appear distorted with swollen cell or compressed, twisted, and folded.
• Rhizoids present
• Long sporangiophores; usually unbranched.
• Sporangiophores originating just above rhizoids.
• Thick-walled chlamydospores (15-30 um in diameter) may form.
• Special fungal stains (GMS, GF, PAS) generally work poorly.
• Rapid growth rate; matures within 4 days.
• Growth is inhibited by cycloheximide.
• Colonies are usually white to cream to gray-pigmented.

Rhizopus is one of the many species of the class Zygomycete, order Mucorales. The sporangium produce asexual spores.The sporangia are spherical, and turn from an initial white color to a blackish brown. They produce grayish-brown spores which spread the disease to other hosts. Rhizopus survives on crop debris in or on the soil between growing seasons. The fungus invades fruit through wounds and uses enzymes to break down and kill tissue ahead of the actual fungal growth. This genus is differentiated from Mucor spp. by the presence of stolons, rhizoids, and usually unbranched sporangiophores. It is differentiated from Absidia spp. by the location of the rhizoids in relation to the sporangiophores and by the shape and size of the sporangia.

The top left picture shows Rhizopus stolonifer under light microscopy (400X).
 

The bottom left picture shows the sporangium of the mold Rhizopus stolonifer.
 
 
 
 
 
 

Rhizopus grows well on general fungal media and frequently fills the petri dish. Rhizopus species may overgrow and inhibit other fungi. Some structures are visible to the naked eye, i.e. sporangia appear macroscopically as black dots in the midst of white, cottony mycelia.
 
 

R. arrhizos grown on potato dextrose agar in petri plates.  The white cottony mycelium have turned a gray color as reproductive structures called sporangia formed.

Rhizopus is found nearly everywhere, but is most prevalent in forest and cultivated soils, on decaying fruits and vegetables, and on animal dung and compost.  It is primarily a parasitic plant pathogen, causing Rhizopus rot.


Rhizopus rot, caused by Rhizopus nigricans, can be very destructive to harvested fruit. It most commonly affects fruit in storage, during transit, and at the marketplace.  Peaches, nectarines, sweet cherries, strawberries, and plums are most susceptible.  However, Rhizopus rot may occur on all decaying vegetation.  When environmental conditions are not favorable, it produces thick-walled zygospores that can withstand long periods of cold and drying.  These are present on dead vegetation, in used fruit containers, and in packhouses and storages.  Thus, some type of spore of the Rhizopus rot fungus is always present where fruit is handled.but is not limited to vegeatative material.  A few species of Rhizopus are known to cause disease in humans as well. Rhizopus oryzae is the principal cause of zygomycosis, which occurs primarily in patients suffering from diabetic ketoacidosis (rhinocerebral disease), malnutrition, severe burns, or who are immunocompromised. 

Rhizopus Rot on a peach (above image).

Campbell, Mary C., and Joyce L. Stewart.  1980. The Medical Mycology Handbook. John Wiley & Sons.  New York.     436 pp.

Larone, Davise H. 1995. Medically Important Fungi:  A Guide To Identification.  American Society for Microbiology Press. Washington, D.C. 274 pp.

5. LINKS TO OTHER SITES ON RHIZOPUS:

A general overview of Rhizopus from the University of Ontario

All you ever wanted to know about Rhizopus rot

An overview of Rhizopus' commercial applications