PRIMARY AND SECONDARY INDUCTION REQUIREMENTS FOR FLOWERING OF CONTRASTING EUROPEAN CULTIVARS OF LOLIUM PERENNE

T.S. Aamlid¹, O.M. Heide² and B. Boelt³

¹The Norwegian Crop Research Institute, Apelsvoll Research Centre, Division Landvik, N-4890 Grimstad, Norway

 ²Department of Biology and Nature Conservation, Agricultural University of Norway, N-1 432 As. Norway

³Danish Institute of Agricultural Sciences, Research Centre Flakkebjerg, DK-4200 Slagelse, Denmark

The flowering requirements of six European cultivars/ecotypes of Lolium perenne L. ('Vejo', Italy; 'Baca', Czech Republic; 'Barcredo', The Netherlands; Falster, Denmark; 'Einar', Norway and 'Kleppe', Norway) were studied in controlled environments at the As phytotron and Landvik Research Station from 1996 through 1998.  In each experiment, eight or nine plants per treatment were raised from seed for three to five weeks before the start of induction treatments.  The percentage of flowering plants and the number of panicles per plant were used as the main criteria of flowering, while days to heading, culm height and ear length were used as additional criteria.  Daylength extensions were always given as low-intensity incandescent light (PAR 1.5 W m^-1). A first experiment investigated the response of all cultivars except 'Kleppe' to increasing duration of primary induction at 6°C/ 8 h daylength.  Flowering was recorded after transfer to secondary induction in an unheated glasshouse (12-25°C) with natural long days (16-18 h).  The low temperature / SD exposure needed for flowering in 50% of the plants ranged from <3 weeks in 'Vejo' to 5-6 weeks and in 'Baca' and 'Barcredo', 6-7 weeks in ‘Falster and 7-8 weeks in Einar^’.  While panicle production in most cultivars levelled off after 12 weeks of SD / low temperature exposure, the turf cultivar ‘Barcredo’ produced most panicles after 15 weeks.  Although the number of days to heading decreased with increasing length of primary induction in all cultivars, this response was least accentuated in 'Vejo'. The critical temperatures for primary induction of ‘Vejo’, ‘Baca’ and ‘Falster’ in short (10 h) and long (24 h) days were investigated in a second experiment.  The set-up was replicated in time with either 10 or 12 weeks exposure periods before transfer to secondary induction in natural long days.  While 80-100 % of the 'Vejo' plants headed regardless of temperature and photoperiod, critical temperatures for 50% heading in SD and LD were about 16 and 11°C in 'Baca' and 11 and 6°C in ‘Falster’.  On average for cultivars, the highest panicle number per plant was found after primary induction in SD at 6 or 9°C.  Long days during primary induction gave longer ears in 'Baca and ‘Falster’ but had no effect on ear length in 'Vejo'. The critical daylength for secondary induction at 18°C was investigated in plants of 'Vejo', 'Baca', 'Falster’ and 'Kleppe' which had previously been exposed to primary induction at 6°C / 12 h for 12 weeks, and which, according to apical dissection, were still vegetative after this treatment.  The daylength required for 50% heading ranged from 12,5 h in 'Vejo' to 14 h in Baca and 17 h in 'Falster' and 'Kleppe'.  Panicle number and culm height increased, but the number of days to heading decreased with increasing daylength in all cultivars. A fourth experiment examined the requirement for LD cycles (24 h) in primary induced plants (12 weeks at 6°C, 10 h).  After 0, 2, 4, 8, 12 or 20 LD at either 12 or 18°C, plants were moved to a growth chamber (18°C / 10 h) for recording of flowering response.  At 12°C the critical number of LD cycles for 50% flowering was <2 in 'Vejo', 9 in 'Baca', 14 in 'Falster and 16 in 'Kleppe'.  As the corresponding numbers of cycles at 18°C were 2-3, 4-5, 9 and 10, respectively; higher temperatures could compensate for some of the LD requirement in all cultivars except 'Vejo' which showed the opposite response.  At both temperatures panicle numbers levelled off after 12 LD cycles in 'Vejo' but continued to increase up to 20 cycles in the other cultivars.  While increasing number of LD cycles and higher temperature reduced the number of days to heading in all cultivars, ear length increased with increasing temperature in the 'Falster' and 'Kleppe', but decreased with increasing temperature in 'Vejo' and 'Baca'.

In conclusion, the present data demonstrate that the requirements for both primary and secondary induction in European germplasm of Lolium perenne ranges from very low in Mediterranean to relatively high in Scandinavian cultivars.  The data also indicate many conspicuous temperature x photoperiod interactions partly similar to and partly different from those demonstrated in earlier work with other temperate grasses.  These interactions, as well as their implications for, the optimal location of seed production of various European cultivars of Lolium perenne L. will be discussed in a final paper on these data.