Photoperiodism and Vernalization
Photoperiodism
- Definition: Response of plants to the relative length of day and night, affecting flowering.
- Discovered by: Garner and Allard (1920).
- Types of plants based on photoperiod:
|
Plant Type |
Flowering Condition |
Examples |
|
Short-day plants (SDP) |
Day length < critical day |
Rice, Chrysanthemum |
|
Long-day plants (LDP) |
Day length > critical day |
Wheat, Barley |
|
Day-neutral plants (DNP) |
Flower irrespective of day length |
Tomato, Cotton |
- Photoreceptor: Phytochrome controls photoperiodic responses.
- Exists in two interconvertible forms:
- Pr: absorbs red light (660 nm)
- Pfr: absorbs far-red light (730 nm)
- Exists in two interconvertible forms:
Most Kharif crops are short-day plants (SDP) because they are sown in monsoon season when days are long at sowing but shorten during growth, triggering flowering.
Short-Day Kharif Crops
- Definition: Flower when day length < critical day.
- Examples:
- Rice (Oryza sativa)
- Maize (Zea mays) – some varieties
- Sorghum (Sorghum bicolor)
- Cotton (Gossypium hirsutum)
- Chrysanthemum (horticultural crop)
Long-Day Kharif Crops
- Very few Kharif crops are long-day plants; most long-day crops are Rabi crops.
- Example: Some vegetable crops like spinach may respond as long-day under certain conditions, but generally Kharif = Short-day.
Summary
|
Crop Type |
Photoperiodic Response |
Example |
|
Short-day (most Kharif) |
Day length < critical |
Rice, Cotton, Sorghum |
|
Long-day (rare) |
Day length > critical |
Few leafy vegetables |
Tip for exams: Remember: “Most Kharif crops are Short-day plants”; Rabi crops are usually Long-day plants.
Vernalization
- Definition: Induction of flowering by low temperature.
- Discovered by: Melchers and Lang
- Important concepts:
- Devernalization: Loss of vernalization effect due to high temperature.
- Example: Winter wheat requires cold period for flowering.
