Bolting control by low temperatures in root chicory (Cichorium intybus var. sativum)

Experiments where plants were initially cultivated in controlled growth rooms, before transplanting in the field in late April or in early May, strongly suggested that low temperatures were responsible for the high percentages of bolting and flowering recorded in early-sown plants in the field. Effectiveness of a treatment at a constant 4 °C in inducing bolting depended on its duration, on the variety, and on plant age when vernalization started. Greatest sensitivity to cold occurred soon in plant's life, during seed imbibition. Fluctuating temperatures (16 h at 4 °C followed by 8 h at 15 °C) were also able to cause bolting. Vernalization effectiveness was affected by climatic variations after vernalization and the transfer of the plants in the field. The results are discussed in relation to information coming from studies on radicchio and Witloof chicories.