Nicotiana sylvestris flowers only during long days and N.tobacum flower only during short days in the labortory undre different photoperiods , they can be induced to flower at the same time and can be cross fertized to flower aat the and can be corss fertillzed to produce self - fertile offsping .What is the best reason for considering N. sylvestris and N . tobacum to be separate species

Options

A. They cannot interbreed in nature
B. They are reproductively distinct
C. They are physiologically distinct
D. They are morphologically distinct

Answer

To determine the best reason for considering Nicotiana sylvestris and Nicotiana tobaccum to be separate species, we can analyze the information provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding the Species**:
- Nicotiana sylvestris flowers only during long days.
- Nicotiana tobaccum flowers only during short days.

2. **Photoperiod Requirements**:
- The two species have different flowering requirements based on photoperiods (day length).
- This difference indicates that they have evolved under different environmental conditions.

3. **Laboratory Conditions**:
- In laboratory settings, both species can be induced to flower at the same time.
- They can also be cross-fertilized to produce self-fertile offspring.

4. **Definition of a Species**:
- A species is typically defined as a group of organisms that can interbreed naturally and produce viable offspring.
- Interbreeding in natural conditions is a key factor in defining species.

5. **Interbreeding in Nature**:
- Although N. sylvestris and N. tobaccum can be cross-fertilized in the lab, they cannot interbreed in their natural habitats due to their differing photoperiod requirements.
- This inability to interbreed naturally is a significant factor in defining them as separate species.

6. **Conclusion**:
- The best reason for considering N. sylvestris and N. tobaccum to be separate species is that they cannot interbreed in nature due to their different flowering requirements.

### Final Answer:
The best reason for considering Nicotiana sylvestris and Nicotiana tobaccum to be separate species is **they can't interbreed in nature**.

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