The effects of temperature alternations, irradiance level, photoperiod, and day extension light quality on morphogenesis, growth, and flowering of Begonia x hiemalis fotsch

The purpose of this investigation was to study the interactions between a 2 h temperature alternation at the end of the night, day extension light quality, photoperiod, and irradiance level on plant height in Begonia x hiemalis. Furthermore, the effect of a DIFference between day (DT) and night temperature (NT) on stem elongation rate by using an angular displacement transducer was studied. Compared to 2 h temperature increase from 18 to 24 degrees C (18-->24 degrees C), a temperature drop from 19 to 13 degrees C (19-->13 degrees C) decreased plant height when combined with fluorescent lamps as day extension light quality of high red (R) / far red (FR) ratio both at 95 and at 190 mu mol(-2) s(-1) PPFD. However, in combination with incandescent lamps with a low R / FR ratio temperature drop reduced plant height only under 190 mu mol(-2) s(-1) PPFD at 16 h photoperiod. Averaged across day extension light quality, a temperature drop compared to the temperature increase decreased plant height at high irradiance level but not at low level. Under high irradiance, plant height increased at 18-->24 degrees C with increasing photoperiod from 8 to 16 h while the plants treated with temperature drop had about the same plant height at both 12 and 16 photo-period. Plant height was greater under incandescent lamps than under fluorescent lamps, except at 12 h photoperiod and 18-->24 degrees C. Under low irradiation, plant height increased with increasing photoperiod from 12 to 16 h under fluorescent lamps but not under incandescent lamps. Stem elongation rate increased as DIF between DT and NT increased. Plants grown under zero and positive DIF had a greater elongation rate during night than during day, while no significant difference was observed in plants grown under negative DIF. No significant differences in leaf area, dry weight and number of flower and flower buds were found between temperature drop and temperature increase.