Primary and secondary induction requirements for flowering of contrasting European varieties of Lolium perenne

Abstract

The flowering requirements of six European varieties of Lolium perenne L. were studied in controlled environments. In experiments on primary induction, flowering was recorded after transfer to long days (LD) in a greenhouse at 12-24°C. In experiments on secondary induction, primary induction was first accomplished at 6°C/10 h daylength for 12 weeks. When evaluated by the 50% heading criterion, the requirement for duration of primary induction at 6°C/8 h daylength was < 3 weeks in Mediterranean, 5-6 weeks in Central European and 7-8 weeks in Scandinavian varieties. While 'Veyo' (Italy) flowered profusely regardless of temperature or daylength during primary induction, critical temperatures for primary induction in SD and LD were 15 and 11°C in 'Baca' (Czech Republic) and 11 and 7°C in 'Falster' (Denmark). The critical photoperiod for secondary induction at 15°C ranged from 12 h in 'Veyo' and 14 h in 'Baca' to 16·5 h in 'Falster' and 17·5 in 'Kleppe' (Norway). The critical number of LD cycles varied correspondingly. While the Central and North European varieties required fewer LD cycles for 50% heading at 18 than at 12°C, 'Veyo' showed the opposite response. It is concluded that the requirements for both primary and secondary induction of Lolium perenne increase with increasing latitude of origin of the germplasm. In one experiment, 39-87% of the inflorescences came from tillers that were not visible on transfer from primary to secondary induction, thus it is also concluded that there is no juvenile stage in tillers of Lolium perenne.