THE INFLUENCE OF TEMPERATURE AND LIGHT ON SEED-GERMINATION OF RADICCHIO (CICHORIUM-INTYBUS L VAR SILVESTRE BISHOFF)

The influence of two light doses and eleven constant temperatures on g ermination of radicchio (Cichorium intybus L. var. silvestre Bishoff) is described. The photosynthetic photon flux density at plant level wa s 37 mumol m-2 s-1, light was provided applying two photoperiods: 3 h d-1 or continuous light. The results obtained were: (i) temperatures r anging from 15 to 35-degrees-C generally assured a high percentage of germination, but some populations also showed a high number of germina ted seeds at 10 or 12.5-degrees-C. Lower temperatures reduced germinat ion capacity, at 40-degrees-C germination failed. (ii) The temperature strongly influenced the length of time between start of imbibition an d beginning of germination. Optimum temperatures were 27-33-degrees-C, at which germination started earlier (12-36 hours from the start of i mbibition). Temperatures below or above the optimum led to a delay in the beginning of germination. (iii) Once the first seed had germinated , temperatures between 15 and 35-degrees-C had fairly similar effects in increasing germination rate. Below this, the germination rate reduc ed as temperature dropped. (iv) Light interacted strongly with tempera ture; the increased photon dose magnified, reduced or did not alter th e effectiveness of the temperatures, depending on the seed lot. A mode l derived by modifying the Weibull function is proposed to simulate ge rmination times at different temperatures. The model parameters were a lso used to calculate a germination index capable of synthesizing quan tity, uniformity and rate of germination.