Vol. 83 No: 4

Title:
Effect of temperature and photoperiod on the incidence of bulbing and bolting in seedlings of onion cultivars of diverse origin

Author:
KHALID MAHMUD KHOKHAR

pp: 488-496

Abstract:
The effects of temperature and photoperiod on bulbing and bolting in onion (Allium cepa L.) cultivars: ‘Senshyu Yellow’, ‘Jaune Espagnol’, ‘Hygro’, ‘Sito’, ‘Delta’, ‘Australian Brown’, ‘Rijnsburger Balstora’, and ‘Phulkara’ from Japan, Turkey, The Netherlands, The United Kingdom, Australia, and Pakistan were examined under controlled environments in glasshouse conditions in the UK. Plants of each cultivar, at the three-leaf stage, were transferred to a wide range of photo-thermal regimes consisting of six-set point temperatures (6°, 10°, 14°, 18°, 22° or 26°C) and four photoperiods (8, 11, 14 or 17 h d^-1). The bulbing ratio in all cultivars increased curvi-linearly with increasing temperature and lengthening photoperiod. Increasing photoperiod promoted bulbing, while under very short photoperiods (8 h d^-1) no cultivars bulbed, even after 60 d of growth.The time to bulb maturity decreased linearly with increasing temperature and lengthening photoperiod. Under low temperatures, the time to floral initiation shortened with lengthening photoperiods (8 – 14 h d^-1). Under photo-thermal regimes favouring floral initiation, leaf number increased with both increasing temperature and lengthening photoperiod.

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