Potential of onion seed production in a tropical environment
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Most tropical countries near the equator import much of their onion seeds because temperatures are not cool enough to induce optimal flowering. The possibility of producing onion (Allium cepa) seed using artificial vernalization and vernalization under natural conditions at high altitude in Kenya was studied. Cured bulbs of three local and eight recently introduced onion cultivars were stored for 8 weeks at 5 and 10°C in a refrigerated cold room, in a well-ventilated storage room at a high altitude location (Njabini, 2 530 m a.s.l.) where average temperature was 13.4°C, and at room temperature at Kabete (1 820 m a.s.l., 21.9°C). They were grown at four locations for 2 years. Location, varietal, and storage temperature effects and interactions were highly significant for days to flower, stalk height, umbels/plant, 1 000-seed weight, and seed yield. Varietal and vernalization temperature effects were significant for percent germination. Bulbs stored at 10°C had the highest seed yield, followed (in order) by those stored at 13.4,5, and 21.9°C for all cultivars, except Bombay Red, which produced higher seed yield at 21.9°C than at 5°C. Bulbs stored at room temperature at Njabini (2 530 m a.s.l.) flowered in all locations for the 2 years. The results showed that commercial seed yields can be achieved by vernalizing bulbs at high altitude locations for production at medium or low altitudes in the tropics.