Lateral development and florogenesis of a tropical shallot: A comparison with bulb onion

The developmental morphology of laterals and flowers was studied in shallot. Growth analyses and microscopic observations revealed strong similarities in organ development between shallots and bulb onions. However, some significant differences were observed, mainly with regard to the minimum physiological age for both laterals and floral differentiation and to the development of the inflorescence. When grown from seed, the initiation of laterals and the first signs of floral differentiation become evident already after the third and sixth true leaves, respectively, as compared to the bulb onion, which first produces 13 or 10-14 leaves, respectively. The shallot inflorescence can be described as an umbel-like flower arrangement, where branches (flower clusters) arise from a common meristem. Leaf formation continues at the axillary meristems in shallots simultaneously with floral development of the original apex. In blooming onion, however, the lateral meristem develops into an adventitious dormant bud. A detailed description of shallot florogenesis and the similarities and differences between blooming shallot and bulb onion are discussed.