Question

How many categories of plants are classified based on photoperiodism ?

• A. Two
• B. Three
• C. Four
• D. Five

Hint:

Photoperiodic Groups:
1. Short-Day Plants (SDP) -- Kharif crops.
2. Long-Day Plants (LDP) -- Rabi crops.
3. Day-Neutral Plants (DNP) -- Photo-insensitive crops.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the primary number of plant categories established based on their photoperiodic flowering response.

Step 2: Concept of Photoperiodism:

• Photoperiodism: The developmental response of plants to the relative lengths of light (day) and dark (night) cycles.

• Three Primary Categories:
• Short-Day Plants (SDP): Flower when day length is less than a critical photoperiod (e.g., Rice, Soybean, Chrysanthemum).
• Long-Day Plants (LDP): Flower when day length exceeds a critical photoperiod (e.g., Wheat, Barley, Oat, Spich).
• Day-Neutral Plants (DNP): Flowering is uffected by day length duration (e.g., Tomato, Maize, Sunflower, Cotton).

Step 3: Detailed Explation:

• Garner and Allard (1920) first discovered photoperiodism and grouped plants into these three main categories.

• Although minor specialized intermediate sub-classes (like Long-Short-Day or Short-Long-Day plants) exist in research literature, standard plant physiology establishes three fundamental primary groups.

• Thus, the correct classification count is 3.

Step 4: Fil Answer:
Plants are broadly categorized into three groups based on photoperiodism. Hence, option (B) is correct.