Onion Seed Production and Vernalization

• Focus is on the cultivation of onions and condiments, particularly big onions.

Cultivation of Onions and Condiments

• This includes onions and chilies
• Big Onion and Cluster Onion are types of onions being studied

Big Onion Cultivation

• Scientific name Allium cepa
• Covers importance, botany, morphology, climatic requirements
• Also covers recommended varieties, physiology of growth, factors affecting bulb formation, and true seed production
• Pungency is a vital ingredient in cooking
• It is a spice in the East and a vegetable in the West
• Traditional medicine, aiding digestion, and preventing muscle pain
• Rich source of Phosphorus, Iron, and Vitamin A
• Good income source

Botany of Big Onion

• Family: Amarylidiaceae
• Scientific name: Allium cepa
• Stems are formed underground from the apical part of the stem
• Leaf bases convert to sheath and cover the stem.
• Sheaths form the pseudostem.
• Root system is superficial
• Inflorescence is Umbel type with 50-200 flowers and is cross-pollinated
• Seeds are triangular and black seeds, viability is less than 1 year
• Biennial plant, but grown as an annual

Ecological Requirements

• Best adapted to DZ during Yala, also LCIZ
• Long days are favorable for bulb formation
• Requires 750mm of rainfall during the growing season
• Need a dry, sunny weather of about 1½ months at crop maturity
• Greater than 70% Relative Humidity may induce diseases
• Prefers sandy loam or Reddish Brown Earth
• Optimum pH is 6.5 - 7.8

Recommended Onion Varieties

• Varieties are recommended for Sri Lankan conditions based on high yield, seed setting ability, storage adaptability, pungency and color
• Pusa Red variety was developed at New Delhi, India, and well-adapted to the Dry Zone (DZ) of Sri Lanka
• Matures in 90-100 days
• Average yield is about 20-25 t/ha
• Has high pungency and a light pink color
• Rampure is a variety developed in India, well-adapted to the Dry Zone, and matures in 85-90 days
• Yields about 15-20 t/ha
• Has better storability, light pink color, and high pungency
• Agri-found Light Red is an Indian variety selected by mass selection and well-adapted to the Dry Zone
• Grown as a Yala crop under irrigation with pink bulbs
• Matures in 90-100 days
• Average yield is about 15-20 t/ha and has good storability/keeping quality
• Kalpitiya selection has slightly pink bulbs and medium pungency, matures in 85-90 days
• N 53 matures in 90-100 days, having dark red bulbs and high pungency
• Nasic Red is mainly cultivated as a vegetable with dark red color and poor storability
• Bombay Red variety has harvest in 90-100 Days After Planting (DAP), having dark red bulbs and high pungency with moderate storability
• Dambulla Selection: locally produced and recommended variety
• Harvest in 85-90 DAP
• Light pink color bulbs
• Potential bulb yield is 30 t/ha, and potential seed yield is 650 kg/ha
• High pungency with good storability
• Suitable for true seed production in Sri Lanka.
• Mibo 1 is a newly released variety

Physiology of Growth and Yield Formation

• The seedling development starts with a tiny embryo constituting 1/10th of the seed.
• Germination occurs in 3-4 days at an optimum temperature of 21-27°C.
• The optimum sowing depth is 6-12 mm, deeper burial hinders seedling emergence
• The vegetative phase occurs from germination to the fourth leaf stage
• Maximum stem thickness is reached
• Thickening of the basal part of the plant indicates bulb formation

Factors Affecting Bulb Formation

• Mainly a long day crop, preferring 12-15 hours of daylight.
• Temperature impact couples act with day length
• Warm temperatures and long days enhance bulb formation.
• Cold temperatures with short days enhance leaf growth and reduces bulb formation
• Optimum temperature of 30-35°C
• High rainfall at maturity can cause serious damage and rotting of bulbs
• Sometimes, Ethephon (2-chloroethyl phosphonic acid) is used to overcome this, applied as a foliar spray
• Accelerates bulb maturity
• Large plants produce bigger bulbs
• Nitrogen has an antagonistic effect; its application should be cut down after the vegetative phase
• Low temperature induces bolting
• Temperatures under 10°C results in immature bolting
• Remove flower stalks manually at the initial stage

Big Onion Bulb Production & Management

• Starts with true seeds in a nursery
• Small seeds with an embryo size of 1/10 require a nursery for healthy, vigorous seedlings and easy supervision
• Low seed requirement of 6-7 kg/ha needed when high quality seeds are used
• Sequential cultivation of onion for seasons increases soil pathogens
• Nursery Bed Preparation is: Size - 3 m x 1m x 15 cm; Need 150 beds to provide seedlings for 1 ha
• Seed treatments like Thiram/Captan at 4-6 g/kg of seeds or Homai at 4 g/kg
• Depth of sowing is 1 cm with rows 10-15 cm apart
• Rate is 7.5-8.5 kg/ha or 40-50 g/bed
• One kg of seeds is enough for 14-15 beds
• Cover with straw mulch after seed sowing
• Inorganic fertilizer applied one day before sowing consists of Urea, TSP, and MOP
• urea 15g, TSP 30g, MOP, 15g
• for high sandy soils, only add TSP-30g, then after 2 weeks add 15 g urea and after 4 weeks add 15 g of MOP
• Cover beds to protect from heavy rains as well as sunlight during initial stage
• If poor growth occurs, add 15 g of urea per gallon of water per bed
• Best time for seed sowing is Mid-March to mid-May
• Nursery period is about 1 month (35-42 days)
• Hardening of plants should begin 10 days before transplanting
• Land and bed preparation includes mainly raised beds, or sunken beds for dry areas with good drainage and sandy soil

Kalpitiya field planting

• No bed preparation necessary
• Planted directly on flat lands
• Add well-decomposed cattle manure (10-12 t/ha)
• Seedlings for transplanting should be 4-5 weeks old, have at least 3 leaves, and be 15-18 cm tall
• Alternatively, dry sets are transplanted
• Dip seedlings in a fungicide solution for about 5-10 minutes before transplanting
• Spacing of 10 cm x 10 cm / 8 cm x 8 cm is recommended, with roughly 100-156 plants per square meter
• For areas except Kalpitiya, fertilizer is applied at a rate of 65-65-65 kg/ha of Urea at 3 weeks after planting and 50-0-25 kg/ha of MOP at 6 weeks after planting
• But for Kalpitiya kg/ha ammonium sulfate 150 / urea 65 / urea 65 , 100 / 0/0 TSP and 50 / 0 /25 MOP kg/ha
• Maintain moisture in bed up to about 2-3 inch depth during the 1st week after transplanting
• sandy soils should be watered twice a day
• From the 2nd week, water once every 3-4 days
• Stop irrigation 2 weeks before harvesting

Irrigation Methods

• Most popular in the Dry Zone, constructing bunds around 3-4 beds in each draining
• Flooding is mainly for sunken Beds

Micro Irrigation Methods

• Applying water directly to the root zone
• Can reduce water wastage by 50%
• Reduces spread of disease through irrigation water
• Good method, need only 2/3 of the water requirement of surface irrigation

Weed Management

• Manual weeding should occur at 3, 4, and 6 Weeks After Transplanting (WAT)
• Pre-emergent weedicides can be used

Harvesting and Postharvest Practices for Bulbs

• Harvest 85-100 days after transplanting
• Stop pesticide application 3 weeks before harvesting
• Stop irrigation 2 weeks before harvesting
• Monitor maturity, at 50% leaf fall at neck area
• Press a plank on the leaves, dry
• Harvest the bulb and uproot all bulbs
• Dry under shade for 2-3 days and narrow the neck
• Some farmers add maleic hydrazide to increase life
• Cut leaves and cure the bulbs
• Remove all moisture from the buds
• Tie up bulbs with trees
• Use dried leaves and ventilated shed racks

Storing & Curing Onions

• Curing increases storability and reduces post-harvest losses
• Well-cured bulbs have sealed neck, 2-3 dried scale leaves, and shiny bulbs
• Onions need to be stored for 1-2 months, can supply heat during rainy periods, can store with <80% RH

Storage of Onions

• Average yield is 8-10 tons per acre
• Peak production during August-September.
• Overdoses of Nitrogen drastically reduce the shelf life
• Bulbs could be stored up to 10 cm thickness without affecting the storability
• Medium-sized (50-60 g) bulbs are the most suitable for storage
• Environments with humidity less than 80% and moderate temperatures 20-30°C
• Spray Carbendazim on the crop at a rate of 8 g/10 liters of water two weeks before harvesting to decrease rotting losses in storage
• Thrips is a major pest

Major Diseases

• Bulb rot, purple blotch and anthracnose
• Only certain cultivars produce flowers in Sri Lanka
• Select best bulbs from a Yala cultivation and plant at the end of December to early January during Maha season

True Seed Production of Bulbs

• Onion seeds are mainly imported from India.
• Select true-to-type bulbs weighing 60-80 g
• Store bulbs in a 1 1/2 to 2 months before planting and ventilated.
• They must be stored for two months before planting
• Can produce seed requirement for 1 acre by 300-500 mother bulbs
• Plant mother bulbs on raised beds with spacing of 22.5 x 22.5 cm
• The crop should be covered with white polythene at 3 ft height at rains and nights
• Mature seeds can after planting for 3 months
• Seeds must be well dried, if not germination ability will lose quickly

True seed production under poly-tunnels during Maha season

• Protects against rainy weather during December to April
• Higher true seed yield can be obtained
• Local big onion seed production in Dambulla
• 30,000 kg of bulbs are used in 10 acres to obtain 2000 kg of seeds

Preparation of Mother Bulbs

• Vernalization: Store at 10-15 Celsius to produce more flowers for about 3 weeks before
• It induces buds
• Also harvest one time
• Use small cured dry bulbs obtained from nurseries after 8-10 weeks
• Production of dry sets: Prepare nurseries in May and June
• Apply urea + MOP in 1 gallon of water (4½ l) 3 and 5 weeks after sowing - apply water to wash off the remaining fertilizer on leaves
• Stop watering when plants produce about 1 cm diameter bulbs
• After 2 weeks, carefully press the leaves in a wooden plank
• When the Leaves are dry, uproot plants
• Tie up bulbs with leaves etc use after 6 -8 weeks

Explore the role of vernalization in onion seed production, including temperature ranges and storage of mother bulbs. The quiz focuses on fertilizer application, plant density, and the distinction between 'Big Onion' and 'Cluster Onion'. It also covers planting depths and other practical considerations.