Question

In which one of the following conditions tobacco plants do NOT flower?

• A. Long uninterrupted dark period.
• B. Long uninterrupted light period.
• C. Short light period with long uninterrupted dark period.
• D. Long dark period is interrupted by a flash of red light (660 nm) and immediately followed by far red light (730 nm).

Hint:

Short Day Plant rule: Long night = flowering. Break the night → No flowering.

Answer 1

The Correct Option is B

Concept:
Tobacco is a short day plant (SDP). Short day plants require a long, uninterrupted dark period to induce flowering.

Step 1: Understand photoperiodism.
• Short day plants → Flower when night (dark period) is long
• Light interruption during dark period → Inhibits flowering
• Far-red light can reverse the effect of red light

Step 2: Analyze each option.
• (A) Long uninterrupted dark period → Promotes flowering in SDP \checkmark
• (B) Long uninterrupted light period → No long dark period, hence no flowering $\times$ (Correct answer)
• (C) Short light period with long dark → Promotes flowering \checkmark
• (D) Red light interruption reversed by far-red → Restores dark condition → Flowering occurs \checkmark

Step 3: Conclusion. Thus, tobacco plants do NOT flower when: \[ \text{There is long uninterrupted light period (no long dark phase)} \]