❄️ Thermoperiodism & Vernalization
Study thermoperiodism and vernalization — cold treatment effects on flowering for CUET Agriculture. Went experiment and devernalization covered.
Thermoperiodism
Thermoperiodism is the response of plants to alternating day and night temperatures. While photoperiodism deals with light duration, thermoperiodism focuses on how temperature fluctuations between day and night affect plant growth and development.
- This concept was coined by Went in 1944, who studied tomato plants extensively and found that they grew best when night temperatures were significantly lower than day temperatures.
- Most plants grow better with lower night temperatures than day temperatures. This is because during the night, lower temperatures slow down respiration (which consumes sugars), allowing the plant to retain more of the food produced during daytime photosynthesis.
- Tomato is the classic example: the optimum temperature combination is 26°C during the day / 17-20°C at night.
- The difference between day and night temperature (called the thermoperiod) promotes better growth, flowering, and fruit quality. This is why tomatoes grown in regions with hot days and cool nights (like certain hill areas) tend to be sweeter and of higher quality.
TIP
🔐
Pro Content Locked
Upgrade to Pro to access this lesson and all other premium content.
Pro
Popular Save ₹100/mo
₹ 99 /mo
₹99 charged monthly · Cancel anytime
- All Agriculture & Banking Courses
- AI Lesson Questions (100/day)
- AI Doubt Solver (50/day)
- Glows & Grows Feedback (30/day)
- AI Section Quiz (20/day)
- 22-Language Translation (100/day)
- Recall Questions (20/day)
- AI Quiz (15/day)
- AI Quiz Paper Analysis (100/day)
- AI Step-by-Step Explanations (100/day)
- Spaced Repetition Recall (FSRS)
- AI Tutor
- Immersive Text Questions
- Audio Lessons — Hindi & English
- Mock Tests & Previous Year Papers
- Summary & Mind Maps
- XP, Levels, Leaderboard & Badges
- Generate New Classrooms
- Voice AI Teacher (AgriDots Live)
- AI Revision Assistant
- Knowledge Gap Analysis
- Interactive Revision (LangGraph)
🔒 Secure via Razorpay · Cancel anytime · No hidden fees
Thermoperiodism
Thermoperiodism is the response of plants to alternating day and night temperatures. While photoperiodism deals with light duration, thermoperiodism focuses on how temperature fluctuations between day and night affect plant growth and development.
- This concept was coined by Went in 1944, who studied tomato plants extensively and found that they grew best when night temperatures were significantly lower than day temperatures.
- Most plants grow better with lower night temperatures than day temperatures. This is because during the night, lower temperatures slow down respiration (which consumes sugars), allowing the plant to retain more of the food produced during daytime photosynthesis.
- Tomato is the classic example: the optimum temperature combination is 26°C during the day / 17-20°C at night.
- The difference between day and night temperature (called the thermoperiod) promotes better growth, flowering, and fruit quality. This is why tomatoes grown in regions with hot days and cool nights (like certain hill areas) tend to be sweeter and of higher quality.
TIP
Think of thermoperiodism this way: Plants "work" during the day (photosynthesis) and "rest" at night (reduced respiration). Cooler nights mean less energy wasted on respiration, leaving more for growth.
Vernalization
Vernalization is the process by which exposure to low temperature (typically 0-5°C) accelerates flowering in certain plants that would otherwise remain vegetative. Without this cold treatment, these plants may never flower or take much longer to do so.
- The term was coined by T.D. Lysenko in 1928, a Soviet agronomist who treated winter wheat seeds with cold before spring sowing and found they flowered earlier.
- Crops requiring vernalization: Wheat (winter varieties), Barley, Rye, Beet, Cabbage, Carrot, Onion. These are primarily Rabi (winter) season crops that naturally receive cold treatment during the winter months.
- Site of vernalization perception: The cold stimulus is perceived at the shoot apex (meristem) — the growing tip of the plant. This means the actively dividing cells must experience the cold for vernalization to occur.
- Duration required: 1-3 months depending on the species and variety. Some varieties need only a brief cold spell, while others require prolonged exposure.
- Devernalization: This is the reversal of the vernalization effect caused by exposure to high temperature immediately after cold treatment. If a vernalized plant is suddenly placed in warm conditions before the effect is "fixed," the cold treatment is essentially undone, and the plant reverts to its pre-vernalization state.
Practical Application
Understanding vernalization has direct practical value in agriculture:
- Winter wheat is sown in autumn; the natural cold of winter provides vernalization automatically, and the plant flowers in spring.
- In warm regions where natural cold exposure is insufficient, seeds can be artificially vernalized by pre-chilling them in a refrigerator before sowing. This technique allows farmers in warmer areas to grow crops that normally need cold winters.
Vernalization vs Photoperiodism — Key Differences
| Feature | Vernalization | Photoperiodism |
|---|---|---|
| Stimulus | Low temperature | Day/night length |
| Perceived by | Shoot apex (meristem) | Leaves (phytochrome) |
| Can be reversed? | Yes (devernalization) | Yes (by altering light/dark cycle) |
| Discoverer | Lysenko (1928) | Garner & Allard (1920) |
| Typical crops | Winter wheat, rye, beet | Rice (SDP), wheat (LDP) |
Key Points to Remember
- Thermoperiodism coined by Went (1944); tomato optimum = 26°C day / 17-20°C night
- Lower night temperatures reduce respiration → more net assimilation → better growth
- Vernalization coined by Lysenko (1928)
- Vernalization temperature: 0-5°C; duration: 1-3 months
- Perceived at the shoot apex (meristem), not leaves
- Devernalization = reversal of vernalization by high temperature after cold treatment
- Crops requiring vernalization: winter wheat, barley, rye, beet, cabbage, carrot, onion
Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| Thermoperiodism — Definition | Response of plants to alternating day and night temperatures |
| Coined By | Went in 1944 (studied tomato plants) |
| Why Lower Night Temp Helps | Lower night temperature slows respiration → plant retains more sugars produced during daytime photosynthesis → better net assimilation |
| Tomato — Classic Example | Optimum: 26°C day / 17-20°C night |
| Thermoperiod Effect | Promotes better growth, flowering, and fruit quality |
| Vernalization — Definition | Exposure to low temperature accelerates flowering in certain plants that would otherwise stay vegetative |
| Vernalization — Coined By | T.D. Lysenko in 1928 (Soviet agronomist; treated winter wheat seeds with cold) |
| Vernalization Temperature | 0-5°C |
| Vernalization Duration | 1-3 months depending on species/variety |
| Crops Requiring Vernalization | Winter wheat, Barley, Rye, Beet, Cabbage, Carrot, Onion (primarily Rabi crops) |
| Site of Perception | Shoot apex (meristem) — actively dividing cells must experience the cold |
| Devernalization | Reversal of vernalization effect by exposure to high temperature immediately after cold treatment |
| Practical Application | Winter wheat sown in autumn → natural winter cold provides vernalization → flowers in spring. In warm regions: seeds artificially vernalized by pre-chilling in refrigerator. |
| Vernalization vs Photoperiodism | Vernalization: stimulus = low temp, perceived at shoot apex, discoverer = Lysenko (1928). Photoperiodism: stimulus = day/night length, perceived by leaves (phytochrome), discoverer = Garner & Allard (1920). |
Lesson Doubts
Ask questions, get expert answers