Detection of floral initiation in broccoli (Brassica oleracea L. var. italica Plenck) based on electron micrograph standards of shoot apices

Abstract

Summary. Detecting floral initiation is fundamental to predicting the ontogeny of broccoli (Brassica oleracea L. var. italica Plenck). Scanning electron micrographs of the apical meristem of broccoli (cv. ‘Fiesta’) were made for the transition from the vegetative to advanced reproductive stage. Seven identifiable stages were observed. During the early vegetative stage (stage 1), the apical meristem was a small, pointed, shoot tip surrounded by leaf primordia. The transitional stage (stage 2) was marked by a widening and flattening to form a dome-shaped apical meristem. In the floral initiation stage (stage 3), the 1st-order floral primordia were observed in the axils of the developing bracts. Further work from a field experiment showed that apex diameter at floral initiation averaged 500 ± 3 m when examined under a light microscope. Apex diameter was not affected by photoperiod, planting time or cultivar. These descriptions and micrographs will enhance broccoli research by standardising the descriptions of floral development in broccoli, and will also be used as the basis of future work in the field identification of floral initiation and the prediction of the timing of phenological events in broccoli.