Assertion: In Ascomycetes and Basidiomycetes well distinct Dikaryophase is present during sexual life.
Reason: During sexual reproduction of Ascomycetes and Basidiomycetes plasmogamy is immediately followed by karyogamy.

Options

A. If both assertion and Reason are true and the reason is a correct explanation of the assertion.
B. If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion and Reason are False.

Answer

### Step-by-Step Solution

1. **Understanding the Assertion**: The assertion states that in Ascomycetes and Basidiomycetes, there is a well-defined dikaryophase present during their sexual life cycle. This means that these fungi have a distinct stage where two nuclei coexist in a single cell without fusing.

2. **Evaluating the Assertion**: The assertion is correct. In the life cycle of Ascomycetes and Basidiomycetes, after the fusion of compatible hyphae (plasmogamy), the resulting cells enter a dikaryotic phase where they contain two nuclei. This dikaryotic phase can persist for a significant duration, allowing for the development of secondary mycelium.

3. **Understanding the Reason**: The reason states that during sexual reproduction in Ascomycetes and Basidiomycetes, plasmogamy is immediately followed by karyogamy. Karyogamy is the fusion of the two nuclei that results in the formation of a zygote.

4. **Evaluating the Reason**: The reason provided is incorrect. In these fungi, after plasmogamy occurs, the dikaryotic phase is established, which is characterized by the presence of two separate nuclei in the same cell. Karyogamy does not occur immediately after plasmogamy; instead, it occurs later when conditions are favorable.

5. **Conclusion**: Based on the evaluation of both the assertion and the reason, we conclude that the assertion is true, but the reason is false. Therefore, the final answer is: **Assertion is true, Reason is false.**