ISHS Acta Horticulturae 433: I International Symposium on Edible Alliaceae
INTERNATIONAL COLLABORATIVE TRIALS TO EVALUATE SHORT-DAY ONIONS |
| Authors: | L. Currah, Sheila M. Green |
| Keywords: | Allium cepa, climate, disease resistance, heat tolerance |
| Abstract:
The development of networks of onion researchers in the tropics is outlined briefly, and the organisation of trials by members of the Tropical Onion Network associated with the Onion Newsletter for the Tropics is described. Seeds of short-day onion cultivars have been provided for trials in national agricultural research systems in the tropics and subtropics since 1990, through a collaboration between the Natural Resources Institute and Horticulture Research International, UK. The highest yields of onions are given by low dry-matter onions of the Grano and Granex types grown under irrigation in cool upland climates near the margins of the tropics, where there is a long dry season. Where these conditions are met, yields approaching 100 t/ha on a plot basis can be achieved, provided that soil and water conditions are not limiting, and that the timing of cropping is optimal. Nearer to the equator and at lower altitudes, overall yields are less: warmer growing conditions result in shorter growth cycles, and the more humid climates of these areas lead to reduced leaf area because of fungal diseases. Red onions, especially those selected under tropical conditions, sometimes perform better than brown, yellow or white onions in the more equatorial environments, suggesting that some of these red cultivars are better adapted to grow and bulb under high temperature and humidity. Needs for onion breeding specifically for the tropics are deduced from the trials results. | |
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