Croissance et tubérisation du radis (Raphanus sativus) selon la durée d'éclairement
Radish tuberization was studied with plants grown in a controlled-environment room at 19 °C day and night, with a daily light duration (radiant flux density, 600 μmol m−2 s−1 photosynthetically active radiations (PAR)) varying from 4 to 24 h at 2 h intervals. Day length did not seem to play a role in the initiation of tuberization: tuber thickening began after about 50 h of cumulative light exposure for all treatments. Moreover, two light treatments with the same daily photosynthetic balance, 8 h a day at high saturating irradiance (600 μmol m−2 s−1 PAR) and 16 h a day at low irradiance (200 μmol m−2 s−1 PAR), resulted in the same growth and tuberization regardless of day length. When the photoperiod is shorter than 7 h, it can modify leaf area, but for longer photoperiods, age is the main criterion determining foliage area. Cumulative light exposure determines the tuber dry matter to foliage dry matter ratio (tuberization index) if the day length is shorter than 16 h; if it is not, plant age alone determines the tuberization index. Day length has an effect on radish tuberization essentially because of its trophic action by photo-synthetic assimilate allocation to tuber thickening.