Zygospores are not generally formed in cultures of Rhizopus developed from a single spore due to :

Options

A. absence of (+) and (-) strains of hyphae
B. presence of (+) and (-) strains of hyphae
C. shortage of nutrients
D. presence of light

Explanation

### Step-by-Step Solution:

1. **Understanding Zygospores**: Zygospores are a type of sexual spore formed when two haploid hyphae (fungal filaments) of different mating types (often referred to as + and - strains) fuse together. This fusion creates a zygote, which then develops into a zygospore.

2. **Rhizopus Overview**: Rhizopus is a genus of fungi that typically reproduces asexually through spores. In the context of sexual reproduction, zygospores can be formed when compatible hyphae from different strains come together.

3. **Single Spore Cultures**: When Rhizopus is cultured from a single spore, it means that only one haploid strain is present. Since zygospores require the fusion of two different haploid strains (one + and one -), the absence of a second strain means that zygospores cannot be formed.

4. **Conclusion**: Therefore, zygospores are not generally formed in cultures of Rhizopus developed from a single spore due to the absence of the necessary mating type (the complementary haploid strain). Without both + and - strains, the fusion required to form zygospores cannot occur.

### Final Answer:
Zygospores are not generally formed in cultures of Rhizopus developed from a single spore due to the absence of positive and negative strains of hyphae.

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