Photoperiod sensitivity in narrow-leafed lupin (Lupinus angustifolius L.)

The influence of photoperiod and vernalization on flower initiation in six genotypes of narrow-leafed lupin (Lupinus angustifolius L.) was investigated under growth chamber conditions to better understand the effect of these parameters in the crop's adaptation to northern European growing conditions. Time to flowering was decreased by long days in all six varieties when these were not subject to vernalization. The combined treatment of both vernalization and long days always resulted in the shortest time to flowering. The effect of daylength was most pronounced in the thermosensitive varieties. In the nonvernalized thermoneutral varieties time to flowering was reduced by 10 to 21 days. There was no flowering in the thermosensitive varieties without vernalization during the 132 days of the experiment. A reduced number of main-stem leaves in nonvernalized treatments in 24-h compared with 10-h days indicates that part of the hastening of flowering in long days was caused by a photoperiod-sensitive flower initiation, and not only caused by increased growth rate. A juvenile, photoperiod-insensitive pre-inductive phase was further established in another experiment where plants were transferred from short (11 h) to long day (18 h) and vice versa at set times. The results showed a well defined juvenile phase of about 35 days where the photoperiod had no effect. After this phase a clear daylength effect was evident both when expressed as time to flowering and as number of main stem leaves developed before flower initiation. Time to flowering was reduced from about 144 days to 65 days and the number of main-stem leaves from 78 to 45. Only a few diurnal cycles in the inductive phase were necessary to reach full photoperiod response.