Vol. 79 No: 6

Title:
Sprouting and yield in bulb onions (Allium cepa L.) as influenced by cultivar, plant establishment methods, maturity at harvest and storage conditions

Authors:
K. GREVSEN and J. N. SORENSENN

pp: 877-884

Abstract:
The use of the sprout-inhibiting chemical maleic hydrazide may be unwanted or banned in bulb onion production.The work reported here was initiated to find alternative production techniques that can reduce sprouting in onions after long-term storage. Field experiments were conducted in Denmark between 1997 to 2001 to investigate the effects of cultivar, maturity at harvest, storage temperature, and transplanting (as opposed to direct sowing) on sprouting tendency after cool storage for 6 to 9 months. Sprouting tendency was measured by shelf-life tests at 15°C.The results showed that use of new low-sprouting cultivars, and early harvest at 20-50% "top fall-down", gave less and slower sprouting in onions after long-term storage. The low-sprouting cultivars were ´Summit`, ´Wembley`, and ´Trafford`. Harvest at 20-50% "top fall-down" postponed the onset of sprouting by 7-10 days compared to harvest at 80% "top fall-down"; but it also reduced the yield by about 15% and the number of large onions. Early harvested onions had a higher dry matter content than late harvested onions. Refrigerated cool storage at 1°C for 8 months resulted in about 5 times lower initial rate of sprouting than storage at 5°C. The use of transplants with 5 seedlings per plug is about 3 times more expensive to establish than direct sowing; but transplanted onions were consistently harvested about 3 weeks earlier, and gave about 10 t ha¹: higher yield as well as larger bulbs. The use of transplants, instead of direct sowing, only resulted in lower sprouting in 2 out of 3 years. The alternative production techniques presented here can reduce sprouting of onions not treated with maleic hydrazide. Published results suggest that a combination of these production techniques and low nitrogen and irrigation treatments can give even higher levels of sprouting resistance.

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