MORPHOLOGICAL AND PHYSIOLOGICAL-ASPECTS OF PHASE-TRANSITION IN RADICCHIO (CICHORIUM-INTYBUS L. VAR. SILVESTRE BISCH.) - INFLUENCE OF DAYLENGTH AND ITS INTERACTION WITH LOW-TEMPERATURE

A series of experiments was undertaken to study daylength control of t ransition to flowering, and interaction between daylength and low temp erature in 'Rosso di Chioggia' radicchio (Cichorium intybus L. var. si lvestre Bisch.). In the experiments, short day (SD) and long day (LD) treatments were variously combined with vernalizing (5 degrees C) and non-vernalizing(> 15 degrees C) temperatures to investigate: (1) the s tage at which photoinducibility is achieved; (2) the number of LD cycl es needed for flowering; (3) changes in LD requirements caused by dura tion and time of cold treatment. Experiments were conducted in control led (growth chambers) and partially controlled environments (heated gl asshouses). Data collected throughout the growth period included perce ntage of bolting, and number of days to both bolting initiation and an thesis of the first capitulum. Additional observations regarded: heigh t and number of nodes of flower-stalk; number and length of lateral sh oots, and number of capitula produced by each plant. Some characterist ic data (leaf number, leaf area, fresh and dry weight of foliage) at t he start of LD exposure were also collected, to study the relationship between developmental stage and sensitivity to daylength. Results ind icate: (1) radicchio can be induced to flower merely by LD, but low te mperature hastens and enhances bolting and flowering. (2) The vernaliz ing effect of low temperature is quantitatively related to the duratio n of cold treatment. (3) Sensitivity to both low temperatures and dayl ength increases with plant age. (4) The stage at which plants acquire maximum sensitivity to cold precedes that at which they achieve maximu m sensitivity to LD. (5) In early growth stages, there is a period of full insensitivity to the photoperiod, i.e., plants must reach a certa in size before acquiring photoinducibility, ((,) Low temperature incre ases plant sensitivity to LD, also accelerating photoinducibility and anticipating the stage at which plant acquires maximum sensitivity to daylength. As vernalization proceeds, fewer LD are required for induct ion-plants exposed to 5 degrees C for 15 or 30 days required more than 10 and 5 LD cycles to flower, respectively. (7) Thermoinduction canno t altogether suppress the:LD requirement in radicchio since? whatever the vernalizing treatment, flowering fails in SD-treated plants. (8) O nce the stage of maximum sensitivity to LD is overcome, photoperiodic sensitivity may diminish gradually, plants reverting to a non-photoind uctive state. This was particularly evident in plants in which vernali zation was suboptimal. (C) 1997 Elsevier Science B.V.