DETECTION OF FLORAL INITIATION IN BROCCOLI (BRASSICA-OLERACEA L. VAR.ITALICA PLENCK) BASED ON ELECTRON MICROGRAPH STANDARDS OF SHOOT APICES

Detecting floral initiation is fundamental to predicting the ontogeny of broccoli (Brassica oleracea L. var. italica Plenck). Scanning elect ron 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 veget ative stage (stage 1), the apical meristem was a small, pointed, shoot tip surrounded by leaf primordia. The transitional stage (stage 2) wa s marked by a widening and flattening to form a dome-shaped apical mer istem. In the floral initiation stage (stage 3), the Ist-order floral primordia were observed in the axils of the developing bracts. Further work from a field experiment showed that apex diameter at floral init iation averaged 500 +/- 3 mu m when examined under a light microscope. Apex diameter was not affected by photoperiod, planting time or culti var. 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 identif ication of floral initiation and the prediction of the timing of pheno logical events in broccoli.