Bulbing of onions (Allium cepa L.): The role of endogenous ethylene*

Abstract Bulbing of onions under naturally increasing daylengths was typically associated with elevated rates of ethylene evolution (10?20 mm³× 10³ g^?1h^?1) during the initial stages of bulbing, followed by a decline to very low rates (1 mm³× 10³ g^?1h^?1) towards bulb maturation. However, detailed comparisons conducted under controlled photoperiodic conditions showed only slight differences in the course of ethylene evolution between inductive and non-inductive lighting regimens. Bulbing was not prevented by hypobaric ventilation or by treatments with the ethoxy analogue of rhizobitoxine, but Ag⁺ interfered with bulbing. Although exogenous ethylene induces bulbing under non-inductive photoperiodic conditions, the role of endogenous ethylene in the natural process requires further clarification.