Question

Which one of the following shows heterothallism?
A. Rhizopus
B. Bacterium
C. Cycas
D. Ricinus

Answer 1

Hint: Heterothallism is a phenomenon in which two different sexes participate in sexual reproduction. It is usually used to distinguish heterothallic fungi, that require two compatible partners to produce sexual spores from the fungi who undergo sexual reproduction from a single organism.

Complete answer:
- In heterothallism, two separate individuals contribute their nuclei to form the zygospore. It means they require mycelia from two different strains to interact for the formation of zygospores while in homothallism, zygospores can be created by the mycelia of only one strain.
- The sporangia of the Rhizopus contains both ‘+’ and ‘-‘ mating type strains. Meiosis is halted until the zygospores are germinated. The gametogonia usually differ in size, irrespective of the mating type. The size difference is mainly because of nutrition.
- Cycas, however, comes under Gymnosperms and they are heterosporous that produce megaspores (forms female strobili) and microspores (forms male strobili) within the sporangia.
- Ricinus is an angiosperm and its reproduction involves a mixed pollination system favoring selfing by geitonogamy and outcrossing anemophily or entomophily.

Therefore, the answer is (A) Rhizopus

Note:
- Rhizopus stolonifer is widely known as a black bread mold.
- It is a very common saprotrophic fungus that attacks a variety of foods.
- Soft rot or leek disease of strawberry, apple, jackfruit, sweet potato, etc is due to the Rhizopus.
- An American geneticist, A.F. Blakeslee was the first one to use the term “heterothallism”.
- Ricinus is said to be a castor oil plant.
- Fungi reproduce by all three modes, sexual, asexual, and vegetative.