Floral initiation and development in three field-grown Allium species belonging to different sub-genera.

摘要

Floral development and inflorescence structure in three Allium species, A. sphaerocephalon, A. rosenbachianum and A. cowanii, were investigated using scanning electron microscopy (SEM). Inflorescence initiation occurred as an enlargement of the shoot apex followed by spathe initiation. Flower primordia appeared at the top of the enlarged shoot apex, and formed basipetally in A. sphaerocephalon. In both A. rosenbachianum and A. cowanii, primary flower primordia appeared in the lower position of the enlarged shoot apex, and formed acropetally. Secondary flower primordia in A. rosenbachianum and A. cowanii were formed basipetally in the lower position of the primary flower primordia, similar to flower clusters, giving rise to the composite inflorescence. A. rosenbachianum had a large number of flower clusters, whereas A. cowanii produced only a few flower clusters. During flower primordia development, the inner perianth primordia and outer stamen primordia appeared almost simultaneously. A. sphaerocephalon and A. cowanii initiated inflorescences in mid-February (early Spring) and early October (Autumn) respectively. Floral development then progressed steadily until their respective flowering in mid-June (early Summer) and late April (Spring). In A. rosenbachianum, inflorescence initiation was started in mid-July (Summer), and floral development progressed slowly until the formation of pollen mother cells in mid-March (early Spring), and bloom started in early May (late Spring)..