Flowering responses to vernalization and photoperiod in annual medics (Medicago spp.)

Abstract

The three processes thought to control flowering times in annual medics (Medicago spp.) are a vernalization requirement, a long day requirement and a high temperature requirement. To examine the first two processes, seed of seven cultivars of six species was vernalized at 1¦C for periods of up to 11 weeks, then grown to flowering under three photoperiods in a glasshouse. To study the third process, the time to flowering of selected treatments from this expcrirnent was compared with flowering data from plants grown in the field at a range of temperatures lower than in the glasshouse. Vernalization and photoperiod caused large shifts in flowering time but the effects varied widely among species. M. scutellata was almost insensitive to both factors but in M. rugosa acceleration of up to 91 days was caused by treatment. Vernalization and short dark periods were additive in accelerating flowering and largely able to substitute for each other. Species flowered almost simultaneously when given their most favourable conditions for flowering. High temperature accelerated flowering in all species studied. However, in species other than M. scutellata it was necessary for a vernalization requirement to be met before this effect was observed. A new finding was that the vernalization response in M. truncatula and M. littoralis was largely reversed after more than 7 weeks of vernalization. This suggests a previously undetected flowering mechanism in these species.