L'unité biologique du bulbe d'Échalote au cours du temps

Abstract

Summary Bulbs from two cultivars ‘Mikor’ and ‘Jermor’ of Allium cepa L. var. aggregatum i.e. were planted in the field either in October or every month from November to April. Glyphosate, a systemic poison that moves through the vascular system, was injected into the tubular cavity of a well-developed leaf from each plant at successive dates for bulbs planted in October and on a same day for those planted from November to April. Glyphosate-induced damages indicated that vascular communication, first global in the bulb recently planted, progressively tended to be restricted to sub-units, each of them being composed of a shoot apex with the generated leaves and internodes and the adjacent adventitious roots. Thus, according to the age of the plant, the unit constituted by the original bulb was split into vegetative sub-systems, each of them being issued from the bud of the initial bulb without ontogenic priority. This deep change indicated a sequence in the developmental stages. A juvenile phase was characterised by a global vascular communication through the whole bulb. It was followed by a maturation stage corresponding to the formation of the shallot tuft, while a somatic generation composed of biological units, i.e. true entities, without any vascular exchange with the other parts of the plant, was emerging. This phenomenon may be sufficient to explain why each bud of the shallot tuft can later flower in an independent and random way.