Transfer of flower induction stimuli to non-exposed tillers in a selection of temperate grasses

The effects of time of tiller emergence on panicle formation and other flowering characteristics were studied in single plants of Scandinavian varieties of Bromus inermis, Festuca pratensis, Dactylis glomerata and Lolium perenne exposed to primary induction at 4°C/LD (24 h), 9°C/SD (10 h) or 15°C/SD. The need for primary induction varied from a predominantly SD requirement in Bromus inermis and Dactylis glomerata to a predominantly low temperature (vernalization) requirement in Lolium perenne and an almost pure low temperature requirement in Festuca pratensis. Although tillers emerging before or during primary induction had the highest chance of becoming reproductive in all species, up to 22%, 15% and 27% of the tillers emerging after termination of primary induction, and thus without direct exposure to SD, became reproductive in Bromus inermis, Dactylis glomerata and Lolium perenne, respectively. In an additional experiment with SD induction at 12°C, detillering during secondary induction increased the flowering capacity of non-directly exposed tillers from 17 to 41 in Bromus inermis. These results are discussed in the light of different hypotheses regarding control of flowering in temperate grasses. It is concluded that indirect induction, i.e. the transmission of flowering induction stimuli from mother to daughter tillers, is more likely after SD induction than after low temperature vernalization.