Vol. 72 No: 6

Title:
The Effects of 12 and 16 Hour Daylength Treatments on the Onset of Bulbing in 21 Onion Cultivars (Allium Cepa L) and its Application to Screening Germplasm for Use in the Tropics

Authors:
K.A. METTANANDA and R. FORDHAM

pp: 981-988

Abstract:
Bulbing in onion is primarily controlled by photoperiod and is promoted by long-day conditions. Cultivars differ in their sensitivities to increasing photoperiods and cultivation of onion in tropical regions is dependent on identifying accessions capable of bulbing under the relatively short prevailing daylengths. The bulbing behaviour of 21 onion cultivars was therefore studied under short (12 h) and long (16 h) photoperiods in controlled environments in the UK and under field conditions in Sri Lanka with the objective of developing simple and rapid screening techniques for identifying cultivars for tropical regions. There was a high correlation between the time taken for bulbing of individual cultivars under 16 and 12 h photoperiods in both environments as indicated by a bulbing ratio of 2.0, bulb scale initiation, and bulb maturity. The sequence in which the cultivars bulbed remained constant under the two photoperiods but the time taken was reduced by between 50–70% under the long 16 h day condition. There was also a high correlation between the time taken to achieve a bulbing ratio of 2.0 (which can be determined non destructively) under an extended 16 h photoperiod, and the time to bulb maturity under tropical field conditions where the prevailing daylength was approximately 12 h. These findings are discussed in terms of their application to screening of onion germplasm and cultivars for use in different regions. The cvs Early Lockyer Brown, Superex and Agrifound Rose were very early maturing followed by an "intermediate" group consisting of cvs Galil, H489, Agrifound Light Red, Red Creole-C5 and H-226, all of which are suitable for production in the tropics.

Full text: JHSB Subscribers     ISHS members & other users
(PDF 434315 bytes)

Translate:

Go back to previous page