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

The flowering requirements of six European varieties of Lolium perenne L. w ere studied in controlled environments. In experiments on primary induction , flowering was recorded after transfer to long days (LD) in a greenhouse a t 12-24 degreesC. In experiments on secondary induction, primary induction was first accomplished at 6 degreesC/10 h daylength for 12 weeks. When eval uated by the 50 % heading criterion, the requirement for duration of primar y induction at 6 degreesC/8 h daylength was <3 weeks in Mediterranean, 5-6 weeks in Central European and 7-8 weeks in Scandinavian varieties. While 'V eyo' (Italy) flowered profusely regardless of temperature or daylength duri ng primary induction, critical temperatures for primary induction in SD and LD wire 15 and 11<degrees>C in 'Baca' (Czech Republic) and 11 and 7 degree sC in 'Falster' (Denmark). The critical photoperiod for secondary induction at 15 degreesC 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 v aried correspondingly. While the Central and North European varieties requi red fewer LD cycles for 50 % heading at 18 than at 12 degreesC,'Veyo' showe d the opposite response. It is concluded that the requirements for both pri mary and secondary induction of Lolium perenne increase with increasing lat itude of origin of the germplasm. In one experiment, 39-87 % of the inflore scences came from tillers that were not visible on transfer from primary to secondary induction, thus it is also concluded that there is no juvenile s tage in tillers of Lolium perenne.