A study of wheat development in the field: analysis by phases

The development of several winter and spring wheat varieties was investigat ed at two sites with up to eight sowing dates from 1989 to 1992. The life c ycle from sowing to ear emergence was considered in phases from sowing to d ouble ridge stage, double ridge to terminal spikelet stage and terminal spi kelet stage to ear emergence, and explanations for the durations of each ph ase were sought in terms of thermal time, effective vernalization days and photoperiod. The life-cycle duration in thermal time from sowing until ear emergence dec lined as the sowing date became later. Assessed using a model function, ver nalization was a major factor affecting the duration of the phase from sowi ng to double ridge stage for winter varieties. Some spring varieties showed small responses to vernalization, Photoperiod affected the duration of bot h the double ridge to terminal spikelet and the terminal spikelet to ear em ergence phases. Some differences among extreme types were detected. The dur ation of the double ridge to ear emergence phases responded similarly to me an photoperiod in two successive years. This finding should prove useful in predicting ear emergence dates. However, the duration of double ridge to t erminal spikelet and terminal spikelet to ear emergence phases at comparabl e photoperiods differed between years. Such differences may arise because t he duration of later phases may also be affected by the environment during earlier phases, particularly the sowing to double ridge phases. Also, earli er phases affected the conditions when subsequent stages were attained; for example, the photoperiod during the double ridge to terminal spikelet phas e was substantially modified by duration of the sowing to double ridge phas es. In view of the importance of early stages of development in crop management techniques, the characterization of differences in response to vernalizati on among varieties is a priority for future research. However, progress dep ends on a fuller understanding of the fundamental mechanisms of response to low temperature. (C) 1999 Elsevier Science B.V, All rights reserved.