• Rhizopus stolonifer is also known as black bread mold.
• Thallus is white cottony, much branched mycelium.
• Mycelium is differen­tiated into nodes and internodes. The nodal region bears much branched rhizoid grows downward, inside the substratum for anchorage and absorption of food.
• The internodal region is the aerial and arching hyphae, known as stolon, which when touches the substratum forms the nodal region

Reproduction in Rhizopus: life cycle

1. Fragmentation
2. Asexual method: Sporangiospore formation and chalmydospore formation
3. Sexual method: gamentagial copulation

 Fragmentation:

• Disjoining of hyphae gives new organism.
• It is one of the common mode of reproduction in Rhizopus

Asexual reproduction in Rhizopus:

• It occurs during favorable condition
• Aerial hyphae develop from internode and arise to certain height
• The nuclei and cytoplasm push more and more towards the apical side, consequently the apex of the aerial hyphae swells up.
• The swollen part enlarges and develops into a large round sporangium
• Sporangium differentiates into two region; multinucleated sporoplasm and vaculated columellaplasm
• Nucleus in sporoplasm divides rapidly, and each nuclei gather some cytoplasm and transform into spongiospore
• After maturity columella collapsed releasing sporangiospore in atmosphere
• Sporangiospore attached to substratum and germinates to give mycellium
• During unfavorable condition, septum formation occurs in mycelium and each intercalary mycelium give rise to thick resting spore known as chlamydospore.

Sexual reproduction in Rhizopus:

• Sexual reproduction takes place during unfavourable condition by means of gametangial copulation.
• Most Rhizopus are heterothallic
• When two mycelium of opposite strain come close to each other, each mycelium produce small out­growth, called progametangia
• The apical region of the two progametangia come in close contact and cytoplasm of each progametangium push more and more towards the apical region which swell up with dense protoplasm.
• The apical region is known as gametangia and basal region is known as suspensor
• The protoplasm in gametangia fuses to from zygospore
• Zygospore is a resting spore
• During favorable condition, spore wall rupture and form germ tube which elongates to form promycellium
• Promycellium have two region; germsporangiophore and germsporangium
• Nucleus in germsporanium divides by meiosis forming haploid nuclei, which gather cytoplasm and behaves as spore.
• The haploid spore are released and germinates to give mycellium

Rhizopus stolonifer:  morphology and reproduction of black bread mold

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