🧅 Onion — India's Most Important Foreign Exchange Earning Vegetable
Complete guide to onion cultivation covering bulb formation, photoperiod response, pungency compounds, varieties, Maleic Hydrazide for storage, thrips management, and purple blotch disease for competitive exams.
At Lasalgaon in Maharashtra's Nashik district — India's biggest onion market — prices fluctuate daily, influencing the cost of this essential kitchen staple across the entire country. Onion is not just a vegetable; it is a politically sensitive commodity. Maharashtra alone accounts for 23.4% of India's onion area and 27.5% of production, and onion contributes a remarkable 77% of India's total foreign exchange earnings among fresh vegetables. Understanding its cultivation science is critical for both farming and competitive exams.
IMPORTANT
Key exam facts: Day length is more important than temperature for bulb production. Temperature is more important for seed production. Pungency is due to Allyl propyl disulphide. Bolting is caused by low temperature. Spray Maleic Hydrazide @ 2500 ppm to check sprouting in storage.
Botanical Identity
| Parameter | Detail |
|---|---|
| Botanical Name | Allium cepa |
| Family | Alliaceae (previously Liliaceae) |
| Origin | Central Asia |
| Rich source of | Vitamin B Complex |
| Pollination | Highly cross-pollinated (due to protandry) |
| Pollinator | Honey bees |
| Inflorescence | Umbellate (umbrella-shaped cluster) |
| Flower colour | White or bluish |
| Anthesis time | 5-9 am |
| Season | Cool season crop |
India's Position in Onion Production
| Parameter | Fact |
|---|---|
| India's global rank (area and production) | 2nd (after China) |
| India's rank in exports | 3rd (12% of world exports) |
| World's leading onion exporter | Netherlands (21%), followed by Spain |
| Leading Indian state (area + production) | Maharashtra (23.4% area, 27.5% production) |
| Biggest onion market in India | Lasalgaon, Nashik, Maharashtra |
| Share in fresh vegetable forex earnings | 77% |
Types of Onion
| Type | Botanical Name | Key Feature |
|---|---|---|
| Common onion | Allium cepa | Single large bulb |
| Potato/Multiplier onion | A. cepa var. aggregatum | Clusters of small bulbs underground |
| Tree onion | A. cepa var. viviparum | Produces small bulbils on top of flower stalk |
Bulb Formation and Photoperiod
Understanding the interplay between day length and temperature is essential:
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At Lasalgaon in Maharashtra's Nashik district — India's biggest onion market — prices fluctuate daily, influencing the cost of this essential kitchen staple across the entire country. Onion is not just a vegetable; it is a politically sensitive commodity. Maharashtra alone accounts for 23.4% of India's onion area and 27.5% of production, and onion contributes a remarkable 77% of India's total foreign exchange earnings among fresh vegetables. Understanding its cultivation science is critical for both farming and competitive exams.
IMPORTANT
Key exam facts: Day length is more important than temperature for bulb production. Temperature is more important for seed production. Pungency is due to Allyl propyl disulphide. Bolting is caused by low temperature. Spray Maleic Hydrazide @ 2500 ppm to check sprouting in storage.
Botanical Identity
| Parameter | Detail |
|---|---|
| Botanical Name | Allium cepa |
| Family | Alliaceae (previously Liliaceae) |
| Origin | Central Asia |
| Rich source of | Vitamin B Complex |
| Pollination | Highly cross-pollinated (due to protandry) |
| Pollinator | Honey bees |
| Inflorescence | Umbellate (umbrella-shaped cluster) |
| Flower colour | White or bluish |
| Anthesis time | 5-9 am |
| Season | Cool season crop |
India's Position in Onion Production
| Parameter | Fact |
|---|---|
| India's global rank (area and production) | 2nd (after China) |
| India's rank in exports | 3rd (12% of world exports) |
| World's leading onion exporter | Netherlands (21%), followed by Spain |
| Leading Indian state (area + production) | Maharashtra (23.4% area, 27.5% production) |
| Biggest onion market in India | Lasalgaon, Nashik, Maharashtra |
| Share in fresh vegetable forex earnings | 77% |
Types of Onion
| Type | Botanical Name | Key Feature |
|---|---|---|
| Common onion | Allium cepa | Single large bulb |
| Potato/Multiplier onion | A. cepa var. aggregatum | Clusters of small bulbs underground |
| Tree onion | A. cepa var. viviparum | Produces small bulbils on top of flower stalk |
Bulb Formation and Photoperiod
Understanding the interplay between day length and temperature is essential:
| Factor | Importance |
|---|---|
| Day length | More important than temperature for bulb production |
| Temperature | More important than day length for seed production |
| Optimum temperature for bulb development | 20-25 degrees C |
- Short-day varieties form bulbs at 11-12 hours of daylight (suitable for South India).
- Long-day varieties require 14-16 hours of daylight for bulbing (suited for temperate regions).
- Bolting (premature flowering / stem elongation) is triggered by low temperature (vernalization) — an undesirable response that reduces bulb quality.
Pungency and Chemical Compounds
| Compound | Role |
|---|---|
| Allyl propyl disulphide | Pungency (volatile sulphur compound causing tears) |
| Quercetin | Colour of outer skin (yellow-brown flavonoid); antioxidant, anti-cancer |
| Catechol | Phenolic compound with antifungal property; protects outer scales |
IMPORTANT
Key pungency compounds to remember: Onion = Allyl propyl disulphide. Garlic = Diallyl disulphide. Chilli = Capsaicin.
Post-Harvest and Storage
- To check sprouting during storage: spray Maleic Hydrazide (MH) @ 2500 ppm, applied 15-20 days before harvest.
- MH is a plant growth inhibitor that suppresses cell division in the onion meristem, extending storage life by several months.
- Zinc application (1-3 ppm) increases yield and improves storage quality.
- Onion is traditionally used in sun stroke treatment due to its cooling properties.
Seed Rate
| Method | Rate |
|---|---|
| Seeds (nursery raised) | 8-10 kg/ha |
| Bulb planting | 750 kg/ha (medium-sized bulbs) |
Important Varieties
By Colour and Use
| Category | Varieties |
|---|---|
| Largest cultivated type | Orange and Yellow |
| White (dehydration) | Pusa White Flat, Bhima Shubra |
| Green onion | Early Grano, Pusa White Flat, Pusa White Round |
| Small onion (pickling) | Bangalore Rose, Arka Bindu, Agrifound Red |
| Export quality | Arka Bindu, Agrifound Rose |
| Selfing variety | Pusa Madhvi (unusual for cross-pollinated onion) |
By Development Method
| Method | Varieties |
|---|---|
| Introduced | Brown Spanish, Early Grano, Bermuda Yellow |
| Selection | Pusa Ratnar, Pusa Red, N-53, Arka Niketan, Arka Kalyan, Arka Pragati, Arka Bindu, Nasik Red, Agrifound Dark Red, Patna Red, Bangalore Rose |
| Hybrid | Arka Pitambar (White x Red), Arka Kirtiman, Arka Lalima |
| Male sterile lines isolated in | Pusa Red |
By Season
| Season | Varieties |
|---|---|
| Kharif | Arka Kalyan, Agrifound, N-53, N-241, Arka Pragati (both seasons) |
| Long day | Brown Spanish, Early Grano (yellow, good for salad) |
Disease-Resistant Varieties
| Resistance | Varieties |
|---|---|
| Purple blotch resistant | Arka Kalyan, Nasik Red |
Multiplier Onion Varieties
- Agrifound Red, CO-3, CO-4
Pests and Diseases
Thrips — Most Important Pest
- Scientific Name: Thrips tabaci
- Damage: Tiny sucking insects causing silvery streaks on leaves; severe infestations reduce bulb size
- Management: Acephate 1 ml/litre of water
Purple Blotch — Major Foliar Disease
- Cause: Alternaria porri
- Symptoms: Purple, elongated lesions on leaves and seed stalks; severe cases cause complete defoliation
- Resistant varieties: Arka Kalyan, Nasik Red
Summary Table — Quick Exam Revision
Onion Quick Revision Table
| Fact | Answer |
|---|---|
| Botanical name | Allium cepa |
| Family | Alliaceae |
| Origin | Central Asia |
| India's global rank | 2nd (area + production) |
| India's export rank | 3rd (12% of world) |
| Leading exporter | Netherlands (21%) |
| Leading Indian state | Maharashtra |
| Biggest market | Lasalgaon, Nashik |
| Share in fresh veg forex | 77% |
| Pollination | Cross-pollinated (protandry) |
| Pollinator | Honey bees |
| Pungency compound | Allyl propyl disulphide |
| Skin colour compound | Quercetin |
| Antifungal compound | Catechol |
| Bulb formation | Day length > temperature |
| Seed production | Temperature > day length |
| Optimum bulb temperature | 20-25 degrees C |
| Bolting cause | Low temperature |
| Storage sprouting control | MH @ 2500 ppm |
| Seed rate (nursery) | 8-10 kg/ha |
| Seed rate (bulbs) | 750 kg/ha |
| Major pest | Thrips (T. tabaci) |
| Major disease | Purple blotch (A. porri) |
| Purple blotch resistant | Arka Kalyan, Nasik Red |
| Dehydration variety | Pusa White Flat |
| Selfing variety | Pusa Madhvi |
| Male sterile lines in | Pusa Red |
Summary Cheat Sheet
| Fact | Answer |
|---|---|
| Botanical name | Allium cepa |
| Family | Alliaceae |
| Origin | Central Asia |
| India's global rank (area and production) | 2nd (after China) |
| India's export rank | 3rd (12% of world) |
| Leading onion exporter globally | Netherlands (21%) |
| Leading Indian state | Maharashtra |
| Biggest onion market in India | Lasalgaon, Nashik |
| Share in fresh vegetable forex earnings | 77% |
| Pollination type | Cross-pollinated (protandry) |
| Pungency compound | Allyl propyl disulphide |
| Skin colour compound | Quercetin |
| Bulb formation driven by | Day length (more than temperature) |
| Seed production driven by | Temperature (more than day length) |
| Bolting cause | Low temperature |
| Storage sprouting control | Maleic Hydrazide @ 2500 ppm |
| Major pest | Thrips (Thrips tabaci) |
| Major disease | Purple blotch (Alternaria porri) |
| Dehydration variety | Pusa White Flat |
TIP
Mnemonic — "DAY for BULB, TEMP for SEED": In onion, Day length drives bulb formation, while Temperature drives seed production. This distinction is the most frequently tested onion fact in AFO and ICAR exams.