Effect of temperature on growth and flowering ability of three Jersey shallot (Allium cepa L. group Aggregatum) cultivars

Abstract

SummaryThe effect of high temperatures during storage, and the effect of low temperatures and daylength on growing plants were studied in one half-long-shaped bulb variety (cv.‘Mikor’) and in two long-shaped bulb varieties (cvs.‘Jermor’ and ‘Longor’) in France. The critical physiological age of application of the cold treatment was also investigated. Although high temperatures during storage were confirmed to have a beneficial effect on sprouting and growth, these experiments also revealed that they promoted flowering only in the case of varieties with deep dormancy like cv. ‘Mikor’, and when the bulbs were planted in the field in October. Low temperatures applied to buds that had developed two leaves (i.e., after a growth period of 1 month in a greenhouse) led to the production of inflorescences. The best flowering rates of cvs. ‘Mikor’ and ‘Longor’ (94% and 34% of buds which were growing at the beginning of the cold treatment, respectively) were obtained by growing plants for 3 months in a phytotron under a 12 h photoperiod with day and night temperatures of 10°C and 6°C, respectively, then transplanting them into the field in March. However, under our conditions, planting cv. ‘Longor’ bulbs in the field in October produced similar results. For cv. ‘Mikor’, the results were more dependent on Winter temperatures. For cv. ‘Jermor’, none of the conditions tested led to the development of a consistent number of inflorescences.These experiments show that the chilling requirement varies with cultivar, and that the optimum temperature and duration of the cold treatment and/or photoperiod must be determined for each variety.