RESPONSE OF ONION (Allium cepa L.) BULB YIELD TO DAY LENGTH EXTENSION

An experiment was carried out between October 2007 and March 2008 at the permanent site of the University of Jos (08°53'E, 09°57'N; 1,159 m above mean sea level) to investigate the effect of day length extension on the yield of onion bulb (Allium cepa L. ). Two varieties of onion ('Violet de Galmi' and 'Red Creole') were combined with normal, additional 2, 4 and 6 hours after darkness in a completely randomized design with four replications. The results showed that the mean weight of bulb, size of bulb, diameter of bulb, length of bulb and the mean number of rings per bulb increased with increasing day length extension, ranging from 119.74 g to 223.23 g; 15.39 cm - 25.04 cm; 5.69 cm - 8.60 cm; 4.31 cm - 5.76 cm and 6.13 - 10.25 rings respectively. The variety ''Violet de Galmi'' exceeded the variety ''Red Creole'' in all parameters except the mean bulb length, where it was 4.97 cm as against 5.03 cm in the variety ''Red Creole''. There was significant day length extension and variety interaction on the mean bulb-weight, bulb-size, bulb-diameter, bulb-length and the number of rings per bulb. The variety ''Red Creole'' was observed to be more affected by longer day length extension than the variety ''Violet de Galmi'' in the Jos-Plateau environment. The overall results indicate, however, that the variety ''Violet de Galmi'' might be more suited to the Jos-Plateau environment than the variety ''Red Creole'' in terms of the yield of onion bulb. KEYWORDS : Day length extension, Allium cepa L., Bulb yield