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Onion seed (bulb-to-seed) production

Onion seed production by the bulb-to-seed method is the two-stage process used commercially to multiply true-to-type onion seed. Mother bulbs are produced in the first stage and replanted in a second-stage seed crop whose umbels are harvested for seed.

Principle

Onion is a biennial: it accumulates reserves in a bulb during the first growing season and bolts to flower and seed only after a vernalisation cool period. Random direct-seeding fails to control varietal purity. The bulb-to-seed method selects medium, true-to-type mother bulbs after the first season and replants only those, allowing visual roguing of off-types before the seed-producing umbels develop. The method also separates seed multiplication from market-bulb production, supporting clear isolation.

Implementation

Standard practice follows the NHRDF (National Horticultural Research and Development Foundation) protocol: seed is sown in May-June and bulbs harvested in October-November. Medium-sized mother bulbs (4.5-6.5 cm diameter for big onion, 2.5-3 cm for small onion) are graded and replanted in late October to mid-November, with umbels harvested for seed in April-May. NHRDF requires 1,000 m isolation distance for foundation seed and 500 m for certified seed to prevent cross-pollination by insects. Typical yields are 6-8 q/ha rising to 12 q/ha under favourable weather.

Adoption context

Onion seed production is concentrated in Maharashtra (Nashik, Pune), Karnataka (Chitradurga, Tumakuru) and parts of Rajasthan and Gujarat where the bolting period coincides with dry, mild weather suitable for clean seed harvest. NHRDF and private seed companies coordinate contract multiplication with farmer groups.

Limitations

The two-year production cycle ties up land and capital. Cross-pollination by bees over long distances makes isolation distances binding in dense onion-growing tracts. Weather damage during seed-set in April-May, when pre-monsoon storms can flatten umbels, causes substantial yield variability. Pollinator scarcity in some seasons limits seed set.

See also Organic Vegetable Marketing and other commercial vegetable production entries.

References

  1. Onion Agro Techniques. National Horticultural Research and Development Foundation.