Long Day Control of Flowering in Poa Nemoralis in Controlled and Natural Environments

SUMMARY Flower initiation and development in a local population of Poa nemoralis L. were studied in controlled and natural environments at As, Norway, 59° 40′ N. At temperatures ranging from 6 to 21 °C flowering occurred in long days (LD) only. At 12 h photoperiod the plants remained vegetative for at least 145 d. The critical photoperiod for floral initiation was about 14 h at IS and 21°C, slightly longer at 9 °C. A minimum of two LD cycles was required for floral induction at 15 °C when flower development took place in 12 h photoperiod, while more than four LD cycles were required for flower development in 8 h photoperiod. Viviparous proliferation of inflorescences resulted from marginal LD induction and subsequent flower development in short days (SD). The observed critical photoperiods agreed well with the time of floral initiation in the field, the critical photoperiod being reached as soon as growth is initiated in the spring. It is concluded that P. nemoralis is an obligatory long day plant with no SD or low temperature vernalization requirement.