Inhibition of flower induction on in vitro chicory root explants by hydroponic forcing pretreatment of roots

Fragments of vernalized chicory roots (Cichorium intybus L.) cultured in vitro under continuous light flower almost 100%. When chicory roots were placed in hydroponic forcing before in vitro culture, flowering percentage was reduced by half. The build-up of inhibition during 3 weeks of hydroponic forcing was studied in detail. The third week, in which growth of the chicory head is the strongest, was especially important in the inhibition process. When the root apex was eliminated during hydroponic forcing, flowering inhibition in vitro was weaker. The same observation was made when adventitious roots, developed during hydroponic forcing, were removed. The photoperiodic conditions during hydroponic forcing had no influence on the build-up of inhibition. It is suggested that activity of the apex and, possibly, of the adventitious roots during hydroponic forcing cause the flowering inhibition on chicory root fragments in vitro.