Vernalization and photoperiod responses in wheat pre-flowering reproductive phases

It has been established that photoperiod influences the rate of wheat development well beyond the end of the vegetative phase. Conversely, vernalization effects are still assumed to be mainly during the vegetative phase, The aim of the study was to assess the effects of different combinations of vernalization and photoperiods on the developmental characteristics of wheat pre-flowering reproductive phases under field conditions. For this purpose, three high yielding cultivars (ProINTA Puntal, ProINTA Super and Klein Pegaso) were subjected to two vernalization treatments (unvemalized (V-0) and vernalized during 56 days in a cool chamber (V-56)) and four photoperiod regimes. The photoperiod treatments consisted of the natural photoperiod of the season (NP + 0) and daylength extensions over that of 2 (NP + 2), 4 (NP + 4), and 6 (NP + 6) hours. Photoperiod influenced the duration of early (collar-first node detectable) and late (first node detectable-heading) pre-flowering reproductive phases, reducing their durations as photoperiod increased. When cultivars with strong vernalization response (ProINTA Puntal and ProINTA Super) were not vernalized, duration of the early and late pre-flowering reproductive phases increased and the rate of spikelet in initiation decreased. Thus, when vernalization requirements were not satisfied, the spikelet initiation rate was even slower than the leaf initiation rate (both expressed in a thermal time base). Results showed significant interactions between photoperiod and vernalization (vegetative phase), or clear, though non-significant, trends to interactive effects (late pre-flowering reproductive phase). Thus, the length of vegetative and late pre-flowering reproductive phases changed in response to photoperiod depending on the level of satisfaction of the vernalization requirements. The relationship between the cumulative number of leaves on the main stem and thermal time fitted a bi-linear model whenever the final leaf number (LNf) was large, e.g. when photoperiod was not extended or vernalization requirements not satisfied. Thus, responses during the pre-flowering reproductive phases were accompanied by an increased phyllochron for leaves emerging after the first 7-8 leaves. This study demonstrated with field grown plants that the length of the late pre-flowering reproductive phase in wheat is sensitive to photoperiod and that the response to this environmental factor could be changed by the level of satisfaction of the vernalization requirements. (C) 2002 Elsevier Science B.V All rights reserved.