In vitro propagation of cauliflower using curd microexplants.

Cauliflower (Brassica oleracea var. botrytis) with its distinctive pre-inflorescence or curd is a remarkable member of the Brassica cabbage group. During curd development, intense and repetitive branching leads to a spectacular increase in size and the accumulation of millions of meristems at its surface. Although destined to produce flowers, most of these meristems are capable of regenerating vegetative shoots in vitro, making curd fragments an excellent material for the micropropagation of cauliflower. Most reported methods using these tissues were devised for the production of small clones of vitroplants as the true potential of curd fragments remained highly underestimated. We describe a technique exploiting fully this abundance of meristems and optimized for the large-scale in vitro propagation of cauliflower. The curd surface is first mechanically disrupted to break up the meristem clusters and generate microexplants carrying 1-3 meristems. These microexplants are then cultured at high density 1:100 (v:v) (microexplants:medium) in liquid medium containing Kinetin and indole-3-butyric acid (IBA) and produce thousands of microshoots in 12 days. After selecting the best quality microshoots on a sucrose pad, they are transferred en masse to a rooting medium supplemented with IBA. Four weeks later, rooted microshoots are carefully acclimatized before transfer to the field. This semi-automated protocol is rapid, cost effective, and well adapted for the production of clones of several thousands of plants by a single worker in a short space of time.